@bazza
Apple shipped a major speed boost to the Javascript engine in Mobile Safari in iOS 4.3, though they got slammed — rightly or wrongly — for not applying it to the entire OS. It's not just "going to get faster on Androids, Blackberries, etc", it is getting faster on Androids, Blackberries, iPhones, etc.
The iPhone supports the latest HTML 5 database stuff, for local persistent store, as does Android. Blackberry doesn't.
Even since the App Store launched and Apple stopped saying "HTML + Javascript is the API", they've failed to become more restrictive. Every added restriction on one side, such as the 70:30 rule for subscription content, is balanced by one eased on the other, such as the removal of the C/C++/Objective-C/Javascript rule for apps which allows people to use Adobes development tools if they wish.
To my knowledge, Jobs has spoken out publicly only against Flash. The arguments he made that it offers a very poor user experience on mobile have been backed up by every objective review I've seen of the Android client. I doubt I'm alone in having decided never to download the thing onto my Android phone. His conclusions — to ban Flash from his platform — betray his control tendencies but the initial observations were valid.
So, in response to your post: (i) Apple have been improving their Javascript implementation; (ii) Apple do support local storage for Javascript applications; (iii) Apple's maniacal level of control over the iPhone platform has remained more or less constant rather than being some sort of ever-growing all encroaching beast; and (iv) Jobs has publicly trashed technologies only when they deserve to be trashed (his actions following the trashing being the objectionable bit, not the trashing itself).
History has also shown Apple to be a beneficial contributor to the web ecosystem, being the driving force behind the vast majority of WebKit development (it was forked from KHTML when that project was four years old, which was nine years ago) and the originator of the canvas element and 2d/3d CSS transforms amongst others. As far as I can think, they've done nothing at any time to hurt the development and propagation web standards.
I'd therefore suggest that Javascript will remain just as viable on iPhones as everywhere else in the world, give or take that Apple's Javascript implementation tends to lag Google's in speed increases.