I had two mac.com emails, one I used only for purchases and one I saved as a backup email. Since my wife's initials are the same as mine I gave her my spare email when she needed an Apple ID many years ago.
But when we got the kids iPhones in 2009, and we all needed to sync to the cloud separately, my mac.com was the one we used for family iTunes purchases (since probably 2003). So at that time I had to get a new me.com for syncing my private iCloud data.
I just NEVER liked the me.com, which seems even sillier now that MobileMe is no longer a thing.
My kids still access the mac.com email that is associated with our iTunes store ID, and they can use their .mac alias that they used as little kids on that account. But those mac.com email aliases can never be turned into a full blown Apple ID, which ticked them off when they were forced to get a me.com ID later on.