The trends tend to be different than that.
Let's see, the original iPhone came out with 4gb, 8gb or 16gb
the 3g iPhone came with 8, 16, and 32
the 3gs was available with 8,16, and 32
the 4 is available at 8 and was available in 16 and 32
the 4s is available in 16, 32 and 64 and as it is succeeded it will probably get an 8gb model
While our devices are not iPhones they tend to follow the iPhone storage wise.
I see a plateau at 16 and 32. That span was over 4 years. I imagine that there probably won't be many break-throughs between now and three years from now so the standard sizes will be 32 at the low end with 64 at the high end.
Sprint Galaxy S III
T-Mobile Galaxy S 4G
Petition to make carrier locking illegal