The Windows Home Server portion of the software should be the same version on both servers. You can view that in the console, Settings tab, Resources view. If it's not, use the Update button in the console to apply updates for the server that isn't up to date.
The HP software is at version 2.5 on the older hardware; HP has not released a newer version for that hardware yet. The most recent information on that can be found
here.
I'm not on the WHS team, I just post a lot. :)