Even though 1gb may seem and even be enough it certainly has nothing to do with it just being a tablet, which is why some of the newer Android tablets/phones are now coming with 2gb and the extra gig is certainly making a difference.
As a former jailbreaker I do remember that only having 256 megs was a cripplier on the iPad 1 and even 512 meg on the iPad 2 would get taxed quite often. The way to test was by having the available ram constantly showing on the top right bar along side the battery percentage. And on the iPad 1 it was really easy to drop it below 15 meg and thus start getting some random app closures.
The iPad 2 was a lot better but not perfect by any means and by jumping in and out out apps you can drop the available ram into the danger zone. As for the 1gb of the newer iPads I can't say since I have remained stock however with the retina display, larger footprint of apps, etc. I would imagine the iPad 3 to be on par with the ipad 2 and as to how much the improved graphics and processor have helped the iPad 4, I would hope that it has been a great help but would need some jailbreakers to test both the iPad 3 and 4 for comparison.