Digital wouldn't make much of a difference. Even the Vita can't fall back on that one and it seems to have a much higher digital adoption rate from what little info we have.
Why isn't that happening with the 3DS? There are more gamers out there than ever and the 3DS library looks stronger than the DS at first glance. Nintendo have thrown everything they've got at the 3DS these last two years.
I don't think you can explain away the hammered software sales on account of userbase. As you can see from the figures, the LTDs aren't as far apart as the software sales would suggest.
To be honest, 3DS sales probably need a thirty page thread of their own. For every two posters, you'll get three opinions on how the device is performing.
3DS doesnt have the lineup DS had. No Brain Age or Nintendogs like megahit for a new audience. No huge hype over a new 2D Mario like NSMB had. So no, I wouldnt say the lineup is stronger.