The Cavs are definitely entering (or are already in) a crucial part of their season. They seem to be hitting a bit of a wall (much like the Celtics did, and every team does at some point). The injuries are part of it, but they are also starting to see a tougher schedule than they faced for much of the beginning of the year, and tonight, it looked like Lebron was starting to show a little fatigue.
They are going to have a real test to stay fresh, while still fighting for home court through the rest of the season. The Celtics have already played 4 more games, and have an easier schedule down the stretch. These injuries are certainly not going to help anything.
This is why I think they still should be trying to make a trade before the deadline. Yes, they have been playing great, but they also have been relying on some players who have been very fragile throughout their career (Z, West, Williams, Wallace have all had lots of trouble with injuries). If they pass up the opportunity to upgrade their roster, I think it will be a mistake. Chemistry can only go so far, if your players start going down.