Iceman speaks the truth.
They may not be stronger, but they are unique to that particular application on the car. They have a non threaded pilot tip on the bolt, and are the correct length for use with the carrier bearing bracket. I'm of the old school anal retentive A&P mentality which says to use the SPECIFIED hardware, where specified by the applicable technical reference, or in the case, (R)TFM.
A few years ago, I had to spend a "lovely" New Years Day, underneath a 93 TSi/AWD, drilling one of these bolts out because the previous owner had installed J. Random Hardware Store Bolt in the carrier bearing bracket. Hey it fit, and it threaded in, right? Good to go!! /ubbthreads/images/graemlins/banghead.gif The bolt broke off in the block and I discovered that trying to drill it out while hung the hell over, is a sure fire way to discover new and interesting ways to hate life, and that it really would have been easier to just pull the damn motor out of the car. /ubbthreads/images/graemlins/grin.gif