I figure there must be diffs, because mini was a blend of old and new, rather than an exact replica of iPad 2. For me, there wasn't enough inducement with the blend, especially since iPad 4 came out at the same time.
For me, iPad 2 can store lots of apps -- they just crash with annoyingly increasing frequency, especially with browsing. My preferences are to have multiple tabs open at the same time and to read lots of blogs that are heavy on graphics and such. iPad 2 is struggling with that.
The thing is, my browsing habits haven't changed in the three years that I've been using iPads. But iOS versions, apps, websites, images, etc., have gotten more demanding, and crashes happen with more frequency, even on newer hardware (but are especially notable in older iPads).
I know that my iPad 1s rarely crashed the first year or so that I had them, but demands from apps, etc., we're fewer. I figure there must be firmware probs, too, as with lots of platforms -- the weaknesses become more and more apparent as more and more is demanded. Apple hadn't even introduced its version of multitasking then.