I've built houses for a living and must disagree with you on just a few points.
1. The 24" spacing saves building materials and when properly designed leaves no added risk. Some builders have been using 7/16" OSB for roofing; even on 16" centers with clips, this often leaves a wavy roof. 1/2" plywood with clips will span 24" centers with noticeably less wave.
2. The wood of 20 years ago is virtually the same as the wood of today, with the exceptions that grading has gone down approximately one whole step over the past 50 years and, dimensions have been reduced slightly to provide more yield per log.
3. Oriented Strand Board is highly absorbing; exposure to inclement weather will cause it to swell. Often times it is not noticeable unless you are measuring it or trying to install the above-mentioned roof sheathing clips. Plywood can also have issues with wet weather, mainly with the top ply bubbling after being left in rain storms. Compared side-by-side, plywood has a MUCH greater strength both in shear and compression.
4. Not a disagreement, just an added note. Asking the concrete provider to add fiberglass will increase the strength of your concrete tremendously. It is often used as a replacement for mesh (not rebar).