It's not Jelly Bean specifically; it's your tablet's form factor (7 inches, in this case). I have a Motorola Xoom Wi-Fi model with Jelly Bean 4.1.1 with PS Touch, which works fine (minus a quirky bug I posted a day or two ago).
PS Touch was generally made for 10-inch class tablets. I'm sure that will change, especially with the Nexus 7's popularity. Just have to be patient. You could create an idea but I think I saw confirmation by Adobe on Facebook that they're working on it. Not 100% sure though.
Yes, but it ran on the iPad mini from day one! Not to be whiney, but I'm tired of developers who seem to give priority to iPad. Don't they realize how big of a market they're are neglecting? Stop playing favorites(or whatever), please!
We've just released PS Touch 1.4.1, it should then be possible for you to use it on the Nexus 7 now.