I don't think these test results are anywhere close to accurate. Why is the iPhone 4, which has better specs than the iPad 1, 3x slower in the Canvas test? What OS was used on each device? How many test runs were done, and what was the variation like in each?
this might help answer part of your query (from the comments)-
Timothy Fitz Says:
March 8th, 2011 at 6:38 pm
The iPhone 3GS almost always ends up being the fastest of the iPhones. While the iPhone 4 has a faster CPU, they both have the same GPU (PowerVR SGX 535). While the iPhone 4 has twice the ram (which is fully addressable by the GPU), and could have a faster CPU clockspeed (I couldn’t find reliable sources), at the end of the day the iPhone 4 needs 4 times the fill rate to meet the increased resolution of the retina display, and it doesn’t have even close to 4x the fill rate of the 3GS.