WotC has considered this issue in their design for 4e. Szilard, however, is less than impressed with what he's seen:
Instead, though, Wizards seems to be focusing on giving enemies more attacks through two methods: (1) Giving monsters more attacks (which I've already written about) and changing encounter design such that the default assumption is that there are a number of enemies equal to the number of PCs.
I can see a lot of problems with this. First off, it seriously limits the sorts of foes PC face. Most monsters won't be encountered alone. This will lead to PCs guessing that there's an ambush when they only see the single enemy who has been laid out as bait. It may well also ring false to players that they are always running into things in groups of four.
This is a bit of a surprise and dissappointing if true. With their emphasis on terrain features, it would have been easy to add all sorts of interesting wrinkles to hinder the PCs. Maybe the wizard can't cast lightning bolt because he's too busy using levitate to keep everyone out of the acid. Tunnels full of obscuring mist might force the PCs to spread out in order to find the BBEG, who can then launch hit-and-run attacks at the flanks, engaging only a few of the PCs every round. And that's not even touching on the interesting alterations you can make to monsters that Szilard has discussed in the past.
As always, it comes down to the DM to be creative and make fights interesting. Even with a broad list of abilities, players will usually discover their optimal attack and spam it over and over again until their target falls. That's just the smart way to play, and 4e doesn't seem to change that. The burden of keeping things fresh and interesting, therefore, is squarely on the GM's shoulders. Here's hoping the 4e DMG is full of neat ideas and inspiration to help lighten that load.