I know Solaris is on the way out with 10.1
I also know that v10 is only supported on 32bit flavours of RedHat & SUSE.
Google only told me of this blog which had revolved around Engine 9.2.
--EDIT-- Looks like Ubuntu support for may arrive at 10.1. Ease of use and lower costs on AWS look to be the reasons (over CentOS)