They aren't, IMO. They don't weigh much more (and seriously what kind of commute do you have that weight matters that much? This isn't the tour de france...)
The ride of a decent steel bike is much softer (less harsh) than an aluminum bike. An old steel 10 speed with tension shifters (less fiddly/adjustment prone) is my idea of a perfect commuter bike...
Was about to post the same thing but you said it all.
Steel vs aluminum is like vi vs emacs. People argue about it all the time, but if you just go test ride some bikes you'll find out pretty quite which you prefer.
The ride of a decent steel bike is much softer (less harsh) than an aluminum bike. An old steel 10 speed with tension shifters (less fiddly/adjustment prone) is my idea of a perfect commuter bike...