Are there any benchmarking apps that measure how smooth scrolling is on a certain device? The one thing I think that IOS (and Windows 8 as well) still has over Android even after all these years is smoothness in scrolling. After a while you don't really notice the difference until you start using an iphone side by side and realize just how smooth it should be.

Jelly bean made things better and recently I bought the new Nexus 7 and 4.3 seems to have improved things even more. Aside from just "feeling" it is smoother, are there any benchmarking apps to verify this?
Most of the difference you see is likely the result of an addition to Jelly Bean (initially in 4.1 and tweaked a bit in 4.2 and 4.3) called Project Butter.  It basically consisted of vsyncing all graphics, using triple buffering, synchronizing touch response with the vsync, and working to predict and prepare for your next action.  Those seem like small things, but they make a considerable difference.

You can see a slow-motion side-by-side comparison here.  Both devices are Galaxy Nexuses, one with ICS and the other with JB 4.1.  The difference is rather striking, especially with the quick contacts demonstration at 0:45.

As such, the new smoothness isn't going to depend so much on the hardware but on how much the device manufacture has tinkered with things, such as with HTC and Samsung using their own Sense and Touchwiz UIs rather than Google's stock one, and thus benefiting less from Butter.