We built from SignUpasaService.com from scratch, launched, won AngelHack New York, got featured in TechCrunch, got hundreds of beta users, got inquiries from investors all in 48 hours!
Still think B2E is way bigger market but B2D is definitely a nice niche market with lots of room and more importantly helping developers build faster and better.
We recently launched www.SignUpasaService.com to help Developers build their registration, sign up and even payment pages in less than 2 minutes. One TC article later we already have hundreds of beta users!
I used to suggest landing page but now it seems "don't make me think" can become "don't make me link!" Internet users want everything on one page and having a long squeeze page is the only option rather than putting together a cluttered landing page.
Not exactly fair considering eBay just has an awful website and UX. look at airbnb which is designed well and you will find web and app experience to b similar. Apps might not kill the website but they sure as hell will influence design.
The question is what should you care about?! The hardest part about building a software, especially a start up, is not what to put into software, but what to leave out. Pick your best thing and then stick w it (care the most about it). This may force you to neglect other aspects but make sure the things you care about are focused on and then outsource the other things you can (or put them on back burner).