Being just a user (while involved in a few app's developments, though), I greatly respect developers who make their apps available to a wide range of devices and iOS versions. If I find myself close to downloading an app (take a newspaper, for example) and I already see that it requires iOS 6, a compass and whatsoever, while I still use an iPhone 4S and run iOS 5 (because it is my choice), I get very demotivated of buying that app. It indicates that the developer feels very freely with his device and software policies and it interferes with my ease of use.
There are also those 2D games out there which require a newer iOS version and device than Infinity Blade 1 (iOS 3, 3rd gen iDevices) required, and possibly run on even less FPS. I think it's all about (bad?) code and if there are 3rd party plugins (Flurry Analytics, GLU, etc.) embedded and if so, how many.
Let's take Mika Mobile's games as an example (Zombieville USA, OMG! Pirates, Battleheart, Zombieville USA 2)... they run on every device as long as it has iOS 3, the last two ones require iOS 4 (partly for iCloud sync) and one can barely see a difference in FPS between devices. The graphics are beautiful, the animations epic and the gameplay is just smooth. Yes I love that game (Battleheart), but it is because every aspect of the game just works as intended, and beyond expected.
Long story short, the specs of an app are a benchmark to me and result in me to whether trust and like the developer or not. Trusted devs also tend to get many donations and sympathy bonuses on indie blogs/websites...
PS: Also, not all of us seek for a 3D experience. For me and many other TouchArcadians here, 2D games are often desired since it feels more "right" on a small screen (on an iPad, it's a different story) and it's more casual. I know you cannot compare it directly, but take Battleheart (Mika Mobile, offline, 2D) and Order and Chaos (Gameloft, online, 3D). The experience is way more intense while playing 2D games on small games since most 3D titles struggle with sub-optimal 3D engines and issues (Gameloft recently even released a title based on the Unreal engine, yet it does not look anything like Infinity Blade 1 because they struggle with the engine) and too much detail-ish game design. The only ones I know who present a vivid 3D experience are the Real Racing/Need for Speed: Most Wanted, Infinity Blade, Galaxy on Fire 2 and Anomaly Earth guys, and they might be too AAA and/or exceptional to take them as an example.