I was thinking today and realized what you were referring to talking about glue and velcro. This is actually an integral part of the saddle function. The velcro is very high quality and I've never heard of an issue with it. Essentially, you arrange your shims to fit the slope and shape of your horse's back and they stick together with the velcro on the inside of the larger shim that is actually exposed to your horse's pad/back. Then, you stick the entire setup onto the saddle and you have a fitted shape on the bottom. Yes, the glue and velcro is necessary in order to have an adjustable saddle as such, but they stick really well and are very handy especially if you have more than one horse. As long as they all have the same tree width, you can have a set of shims set up for each horse and just slap on the set you need for your ride.
If the velcro was coming unglued, then you must have been looking at a very used or demo saddle that hadn't been taken care of properly. In addition, that could easily be fixed for a quality saddle. The issues I was referring to was a defect in the tree in saddles built during certain years, but the company is willing to replace any defective trees for around $100. Very few saddles have actually had this issue.