Yeah, there wasn't even any actual exclusive for the DSi, other than the DSiWare stuff. I'm not sure Nintendo really cared, actually, as their focus was on the DSiWare and enhanced retail games.
Which is why the XC exclusivity is really special: there's no doubt the OG 3DS can't possibly dream of running it (N3DS seem to be struggling a bit too). Personally, I'm not expecting lots of exclusives, N3DS is just there to make sure the 3DS keep on selling until their next handheld ready (I'd say not before 2016, my money is still on early 2016).
There is one; the European version of Face Training was DSi exclusive. That's the only retail game from Nintendo though.
Regarding the GBC successor versus revision argument in comparison.
GB/GBC cross-compatible
Beauty and the Beast: A Boardgame Adventure (1999)
Bugs Bunny: Crazy Castle 3 (1999) NA/EU only
Conker's Pocket Tales (1999)
Game & Watch Gallery 2 (1998)
Game & Watch Gallery 3 (1999)
Harvest Moon GB (1998) EU only
NBA 3-on-3 featuring Kobe Bryant (1999)
Pocket Bomberman (1998) NA/EU only
Pokémon Gold / Silver (1999)
Pokémon Pinball (1999)
Pokémon Trading Card Game (1998)
Pokémon Yellow: Special Pikachu Edition (1999) NA/EU only
R-Type DX (1999)
Shadowgate Classic (1999)
Tetris DX (1998)
The Legend of Zelda: Link's Awakening DX (1998)
Quest for Camelot (1998)
GBC only
Alice in Wonderland (2000)
Bionic Commando: Elite Forces (2000)
Crystalis (2000)
Donkey Kong Country (2000)
Donkey Kong Land 3 (2000) JP only
Hamtaro: Tomodachi Daisakusen Dechu (2000)
Hamtaro: Ham-Hams Unite! (2001)
Ken Griffey Jr.'s Slugfest (1999)
Kurby Tilt-n-Tumble (2000)
Mario Golf (1999)
Mario Tennis (2000)
Mickey's Racing Adventure (1999)
Mickey's Speedway USA (2000)
Mobile Golf (2001)
Monster Tactics (2000)
Perfect Dark (2000)
Phantom Zona (2000)
Pocket Soccer (2000)
Pokémon Crystal (2000)
Pokémon Puzzle Challenge (2000)
Pokémon Trading Card Game 2 (2001)
Star Wars Episode I: Racer (1999)
Super Mario Bros. Deluxe (1999)
The Legend of Zelda: Oracle of Ages (2001)
The Legend of Zelda: Oracle of Seasons (2001)
The Little Mermaid II: Pinball Frenzy (2000)
Trade & Battle Card Hero (2000)
Wario Land 3 (2000)
Warlocked (2000)
And for fun here are the 1st party GB games with special palettes programmed into the GBC firmware:
Adventures of Lolo (1992) EU only
Alleyway (1989)
Arcade Classics: Asteroids and Missile Command (1995)
Arcade Classics 2: Centipede and Millipede (1995)
Arcade Classics 3: Galaga and Galaxian (1995)
Arcade Classics 4: Joust and Defender (1995)
Atomic Kid (1990) EU only
Balloon Kid (1990)
Baseball (1989)
Battle Arena Toshinden (1996) NA only
Battletoads in Ragnorak's World (1993) EU only
Donkey Kong (1994)
Donkey Kong Land (1995)
Donkey Kong Land 2 (1996)
Donkey Kong Land III (1997)
Dr. Mario (1990)
F-1 Race (1990)
Final Fantasy Adventure (1992) EU only
For Frog the Bell Tolls (1992)
Game & Watch Gallery (1995)
Game & Watch Gallery 2 (1997)
Game Boy Gallery (1995)
Game Boy Wars (1991)
Golf (1989)
James Bond 007 (1998)
Ken Griffey Jr. Presents Major League Baseball (1995)
Kid Icarus: Of Myths and Monsters (1991)
Killer Instinct (1995)
King of the Zoo (1990)
Kirby's Block Ball (1995)
Kirby's Dream Land (1992)
Kirby's Dream Land 2 (1995)
Kirby's Pinball Land (1993)
Kirby's Star Stacker (1997)
Magnetic Soccer (1992)
Mario's Picross (1995)
Mega Man: Dr. Wiley's Revenge (1991) EU only
Mega Man II (1992) EU only
Mega Man III (1993) EU only
Metroid II : Return of Samus (1991)
Mole Mania (1996)
Nigel Manshell's World Championship Racing (1992)
Nintendo World Cup (1991) NA/EU only
Othello (1990) EU only
Pac-in-Time (1994) EU only
Picross 2 (1996)
Pinocchio (1995)
Play Action Football (1990)
Pocket Bomberman (1997) NA/EU only
Pokémon Blue/Green/Red (1996)
Pokémon Yellow: Special Pikachu Edition (1998) JP only
Qix (1989)
Radar Mission (1990)
Soccer (1989)
Solar Striker (1990)
Space Invaders (1994)
Star Wars (1996) NA only
Street Fighter II (1994) NA/EU only
Super Mario Land (1989)
Super Mario Land 2: 6 Golden Coins (1992)
Super R.C. Pro-am (1991)
Tennis (1989)
Tetris (1989)
Tetris 2 (1993)
Tetris Attack (1996)
Tetris Blast (1995) NA/EU only
Tetris Plus (1996) NA/EU only
The King of Fighters '95 (1996) NA only
The Legend of Zelda: Link's Awakening (1993)
The Rescue of Princess Blobette starring a Boy and his Blob(1990) EU only
Top Rank Tennis (1993)
Toy Story (1996) EU only
Vegas Stakes (1995)
Wario Blast featuring Bomberman (1994)
Wario Land: Super Mario Land 3 (1993)
Wario Land II (1998)
Wave Race (1992)
X (1992)
Yakuman (1989)
Yoshi (1991)
Yoshi's Cookie (1992)
That took so much longer than I expected! Nintendo originally planned GBC as a stopgap revision and that's pretty evident given most early games are still GB compatible and nearly every single 1st party GB game has pre-set palettes when played on a GBC. Even 3rd party games they picked up for regional release, although only the Nintendo published versions work (JP or NA FF Adventure has no palette for example). When GBC took off and sold ridiculously above expectations (it ended up doing about 50m over 4 years, better than the original GB had ever sold) then Nintendo switched gears and started doing more GBC games while also continually pushing GBA back. The argument that it was a revision that evolved into a successor makes a lot of sense, I think the only comparable other platform would be maybe PC Engine to CD/Duo in Japan.