Doesn't it depend a lot on the game? A well designed game could get a lot more out of a fast SSD.
That said, it's still true that you typically won't see a very big difference. Any SSD can support loading a level in a few seconds. The difference between normal flash and ultra-fast flash won't show up much unless you're aggressively streaming level data off the drive in real time.
And that would likely tank the performance if the game is running from an HDD.
I suspect you could design the storage layer of your game/app/whatever to take into account the performance characteristics of the underlying drive, and adjust your I/O pattern to be more parallel or more serial accordingly.
I also suspect that would not be easy/economical to do within the time/budget constraints of most projects.
The name of the game is minimizing the head movements.
Try the following experiment: find a couple of multi-GB files on an HDD in order to copy them to an SSD.
First measurement: copy the first file then the second (then the third etc...) and sum-up the time.
Second measurement: just drag'n'drop all the files together and measure the total time.
Reboot before each measurement to purge the file cache.
There is serial as in reading byte 1 2 3 4. This is what you're talking about. This is good on any drive and great on hard drives.
There is serial as in read a byte, do a calculation, read a byte, do a calculation. This is what I was talking about. This is bad on any drive and even more noticeable on SSDs.
If you can have all your data in one single 500MB read, that's great. But I wasn't talking about that, because any drive can do a single giant read with good performance.
If you have to do 800 different reads, it's much better to ask for them all at once. You don't want to trickle them out one at a time. This is what my comparison was.