I agree with your statement, but the problem then becomes device troubleshooting. If I were VZW, and was telling the manufacturer that they can put any build on their phone, my next statement would be to tell them that they have to be the one to provide device technical support. This is where bad customer service would take a new form. We would then have the manufacturer tell us "There appears to be nothing wrong with your phone. The problem is on the service end and you'll have to contact VZW". Then you'll call VZW and they'll tell you "Our network is working great in your area. There must be a problem with your phone hardware or software. You'll have to contact the manufacturer."
At this point you'll toss your phone into the deep end of the toilet and go back to the old 'two cans connected with a string' method of communication. I understand technical support for this method is relatively straight forward.