Yeah, a lot of it is perspective.
I came to the Eris from an iPhone 3G and the eris feels perfectly fine to me. Browser is slower, but Apple kinda has the mobile browser thing on lockdown, theirs is so optimized.
I think part of it too is the trend I've kinda seen going on in which software optimization has taken a back seat to hardware. Instead of "how snappy can we get this to run", some devs are just saying "it'll run awesome when the snapdragon comes out so it's okay" lol. (HTC Phone app, i'm looking at you.)
To me, iPhone OS shows the results of good software optimization and polish.
Android is more open to change, to potential, but conversely lacks a bit of the polish and optimization.
Definitely feels more like a tool where the iPhone seems to abstract its "computer-ness" away and be a magic box.
Different paradigms, different people, different preferences.
As for expecting too much (wow, went off on a tangent there) another part may simply be lack of knowledge of the product they're buying. It's an Eris, not the HTC Desire, it's the same cpu as a G1. Sense is amazing and all but you're buying outdated hardware so your expectations of performance should match accordingly. Unfortunately, a lot of people don't bother to research (which is sad in and of itself, to be throwing money around without knowing exactly what it's going to) so I see this happen frequently.
edit: typed that whole thing on my phone. tapatalk ftw