Bolts break when over-torqued along stress risers which are usually and unfortunately a part of the design. One of the most common ways a wedge bolt breaks is at the spot where the small end of the moveable cone sits at the non-thread end of the bolt. This is because the bolt is significantly narrower there than the rest of the bolt. This is how we used to "remove" wedge bolts before someone came up with the technique for spinning them to set the cone and keep it from sliding up the shaft.
However because the wedge bolt is so popular in the construction world there are lots of companies who make them and because of this the quality can really vary. This means that it is very likely that the other place there is a significant stress riser on a wedge bolt, which is the threads, could also break during over-torquing. This is why it is highly recommended when using wedge bolts for climbing that you purchase ones which used "rolled" rather than "cut" threads. "Rolled" threads eliminate this stress riser.
In the case of the bolt on Cataract Corner it is possible that the bolt did break because of a stress riser in the threads.
As far as glue-ins are concerned, yes, someone with experience should place them. The most common way to do this is to drill all the holes at once and when they are done, then go back and glue all the bolts in. One essential step is to save a sample of the glue coming out of the mixing nozzle so that you can ensure that it was mixing correctly and will set up properly. BTW, yesterday, the ASCA just placed an order for 400 titanium glue ins from a company in the UK. They take a 9/16" hole so drilling isn't going to be much fun, but I am sure they would provide the hardware for this effort.