I have also wondered on SSD why would there be a need to separate out data, logs and TEMPDB onto different drives.  I originally thought that was for spinning drives to spread out hot spots.

The trouble I have in having a data drive, translog drive and a TEMPDB drive is that I have a lot of free space on all three so they all three can grow.  SAN people see all of the free space and think I am wasting it.  I tell them, trans logs can grow greatly for spike usage.  Also, TEMPDB can as well for sorts and rebuild indexes.  They simply see it as allocated and not used space.