You must be a religious person, considering you believe in "promises".
Or just someone who expected people to keep their word. And personally I don't remember Epic making promises but then flaking out on them before the Linux/OSX port debacle. Maybe that's just glasses tinted rose with nostalgia, though, but I don't think so.
We know it uses OpenGL (which UE3 already supported, just a different spec) and it likely uses OpenAL (which has iPhone builds already). I have no idea on the physics portion, but if it has the same editing tools and the same script loading ability... then what else is there really?? It obviously has a more limited feature set but that doesn't make it not the same engine, it just makes it a more limited version of the same engine
Off the top of my head the thing I'd say would be most changed (with the caveat that I have no idea how this kind of low-level code works, or how much of the Unreal Engine these days is abstracted) would be that this is a version that works on ARM! That's an entirely different architecture than we've ever seen the Unreal Engine on before, unless I'm seriously missing something (which I very well might be). So far for the current generation we've basically only seen it on Windows (x86) and the two more powerful PPC consoles (ie. 360 and PS3), along with Gears 1 for OSX. So as you've mentioned we've seen ports using OpenGL and OpenAL before; jumping to ARM is the big technical change from what I can see.
I'd like to chime in on how absurd it is that there's no Linux port of the current engine, despite the fact that they've not only already overcome the obvious technical hurdles with other ports and that they've ported to entirely different CPU architectures!
I wonder what the other platform will be. Windows Mobile, PSP, Symbian, Android ...
I wouldn't be surprised if it turns out to be Windows Mobile or Zune HD (or both). In terms of technical aspects they aren't terribly different from the iPhone; the WinMo and ZuneHD platforms are both ARM-based AFAIK, and Epic already has a fairly tight-knit relationship with Microsoft these days (and I actually say that with no malice, believe it or not).
In theory the Zune HD has a very powerful graphics processor, which might seem to suggest that it'd be a good candidate for porting to, but on the other hand WinMo is a much bigger market. Both platforms are WindowsCE based, however, so I wouldn't be surprised if they released for both of them. Plus this way Epic would get a wide cross-section of the smartphone crowd (in North America, at least) which would give their engine a lot of allure.
Partially I'm betting on WinMo and/or ZuneHD just because in terms of the platform they're the closest out there to the iPhone in technology+ecosystem (especially since they were demoing this on an iPod touch, to which the Zune HD is a competitor). Nonetheless I'd laugh my ass off if the second platform turns out to be Android. Although it'd be a bitter laugh . . . although then I'd immediately start researching how one might run an Android application in a normal Linux install. Even if just for the sheer, palpable irony of it all.