I'm curious on why a developer would want to pay for your solution to what seems like a problem that most can easily solve themselves with very little investment ? (Dynamic updates, pre-caching HTML/JS and presenting it locally for rendering).
The second component you offer on first blush is the JS wrapper / bridge to the native UI widgets which although might be nice to have most seasoned developers may find it a hard sell.
Cross platform would be compelling although the concern there being that the JS bridge is (obviously) iOS centric and may be difficult on other platforms ( Android / Blackberry / win 7 ).
Like I said, looks great I'm just curious what the value add would really be for a high volume application where cost to develop would be less than the pricing you offer (which is also of course recurring).
However about the idea that people can easily build this themselves, I'm not quite convinced. I think it's possible to build 70% of the solution in a short amount of time, but that last 30% is so very fiddly (speaking from experience here.) Some of the big apps have built their own versions of this, and have gotten a piece of it wrong or have learned hard lessons along the way. It's things like race conditions when syncing, reducing bandwidth by downloading intelligently, etc.
The other thing is that this is just the tip of the iceberg. The plan is to solve these same problems on Android, and then to include a comprehensive A/B testing suite, to build drop-in frontend components on top of this platform, and other cool stuff.
A lot of PhoneGap/Web View apps are second rate on the UI front, so if you can help developers improve that experience without a lot of work I'd say you're onto a winner.
I also think you're on the right track with your A/B testing plans - doing this from scratch can be a huge chunk of work!