It's functionally even less than that. Due to the time zone difference, the only place you really see an extra 10 people worth of population is on the Auction House. For all other purposes (siege, instances, chat banter) we're still fairly isolated.
Might be different for people who can play during the workday, but my experience has been that remarkably little changed in my RoM experience post-merge, with the notable (and yes, hugely important) exception of having a working AH.
The upcoming merges won't have this time zone issue and will also presumably involve larger incoming populations, so we can probably look forward to them making more of a difference.