Most people I've dealt with don't like the rough surface that you get from treated 2by6s or 2by4s(which also cup and bow). They would rather have the smoother side of a 5/4 board (which costs more than a 2by) and as long as you put them over properly supported joists on 16" to 24" centers they do just fine. Most deck bounce problems I see are from poorly supported joists. They usually go to the limits on span tables to save digging post holes and don't use any cross bracing. Houses are built all the time with 3/4" floors on joists that are usually 16" centers. It is the foundation that counts. When looking at a typical book deck plan (or from home cheapo), I usually add an extra support or two to shorten up the spans, go to a bigger board (such as 2by8 instead of 2by6) and throw in some extra joists to get close to 16" centers. Of course that is extra lumber cost and labor and the cost of screws goes way up but still cheaper than trex which is about double the cost of treated lumber. The trex demos I see are inside the store and Steve probably has the answer why.