I'd say one thing that make HCI/UE patterns so challenging is the referent context must encapsulate both subjective definitions for interaction, as well as many changing objective limitations (browsers, HTTP, javascript, flash, underlying data portability).
Not sure I understand this correctly. Are you saying that the pattern itself needs to describe or detail things like browser, HTTP, Javascript, Flash, etc? Or are you saying that what makes UI patterns more difficult is that when designing a UI pattern, we have to think of and accommodate for these items?
If the latter, I agree. If the former, then I'd disagree. I've designed dozens of pattern libraries for clients w/o detailing out the specifics of HTTP, Javascript, and Flash.