There's a little more at the link, as well as other posts that reconfirm this claim.
Are we talking about playable choices, drivers, vehicle forms, which platform are we talking about, what?
Me, I go with actual playable choices on the character select. Over all the different platforms, this totals up to 29 actual playable choices. But that doesn't mean that there are 29 playable choices in all platforms (in fact no single platform has all 29). Some drop down to the low 20's, some instead have high 20's.
Why is this? Well some platforms have characters that are unique to that platform. I'm not going to say which, that's part of the fun of the reveals! Some are SEGA characters, some are not. Don't bother asking :P
Playable choices doesn't necessarily equal drivers either. Not as we're talking passengers or hood ornaments, counting those would indeed be cheap, but you know this is game all about transformation, we are doing things with the vehicles that we've not shown you, that are going to really surprise you.
Let the predictions begin!
Edit: I meant "characters", where's the mod-signal when you need it?