Not trying to diminish the use of multiple cursors (I have certain fondness for them despite not using them extensively due to my choice of editor), but using regexes you can still do that (i.e. with /^/ and /$/, which I use constantly with vim-style search and replace)
Pressing ctrl-d a couple of times, seeing what will change, and typing something is most of the time easier and faster than thinking about a regex. At least that's how I feel
Yep, I can see that being easier depending on what you prefer, I just wanted to point out that the feature wasn't unique to multiple cursors, since it was being described as "find and replace on steroids".