There are several misnomers within this thread OP. First of all, there is no way that aluminum can "hold up better to the abuse", than steel framed MTN bikes. Aluminum framed MTN bikes are usually slightly lighter and give a stiffer ride. Most MTN bikers appreciate a stiffer and lighter ride, due to the fact that they feel that they have a greater ride response in both handling and speed.

Also, bicycles made of chromoly steel, are rarely more than a pound or two greater than their aluminum counterparts. In fact, when it comes to your lower end, entry level bicycles there some cases where aluminum bicycle frames even weigh more than their steel counterparts. When we get into the higher end road bikes, you'll get to observe the state-of-the-art highest grades of chromoly steel, such as the 853 and the 631 series. These are the lightest of steel frames and can easily compete with the lighest of aluminum framed road bikes.

When it comes to the durability and resilience of MTB frames, it's more about design and construction, than the material, itself.

Of course, it is easier to abuse an aluminum frame, than a chromoly steel frame....

* Any experienced welder, certified in both MIG and TIG welding, should have no problem repairing the bicycle. Hopefully, he will have some brazing experience, as well.