If the final version on iCloud is as you describe, this is a deal breaker for me then. Lack of feature parity, and inadequate treatment of missing features / fonts / etc. on the iOS side, is the main reason I don't use iWork on my iPhone, and it has been a major factor in my not buying an iPad yet.
It sounds like the web version is basically going to be like the iOS version if you create a document on iOS or the Web, you will be able to use it on the Mac version without a problem. If you create it on the Mac and try to edit it online or on iOS, your mileage will vary.
I create or edit dozens of new Pages documents and a couple Keynote presentations in a given week. Some of them rely on very specific layouts and spacing. Even with using standard fonts, sometimes in my very limited testing, it just didn't work right either errors about compatibility, or it not showing up correctly even without an error. I don't have the time or inclination to try to "fix" what wasn't broken before.
This was about a year and a half ago, but since no major update has been issued and now incremental releases IIRC haven't said anything about addressing such issues, and based on comments I see from time to time (including on this thread), I assume it's still the case for iOS. I am still eager though to try out the beta on iCloud and see what happens.
I realize it is quite a feat to get this all working in a browser, but they've had years to work on the iOS side and presumably have been working on the iCloud version for some time now. If there can't be feature parity, there has to be better treatment of problems and incompatibilities when they arise on iOS and iCloud. If it's a programming hurdle to overcome, I hope they're able to do so. But hopefully they are not leaving out features deliberately to encourage people to purchase the more feature-rich Mac version.
I only use Word & PowerPoint when I have to, and haven't used Google docs for document creation. I am hopeful that the promised new version of iWork will include improvements not only on the Mac side, but also in iOS, coupled with seamless integration with iCloud. This would make it a lot less likely that I or the people I work with would need to use Office. Shouldn't this be at least part of Apple's goal? Once this is done, then maybe we can finally get (back) collaborative features.