I asked my wife about the ADA Title III Guidelines (part of her professional certification requires knowledge of this subject matter). Hopefully, I remember her answers correctly.
Re: Few handicap parking spaces at BWV:
Valet parking is an acceptable alternative to providing handicap spaces and it is provided free of charge at WDW. There could be zero handicap parking spaces if they wanted.
Re: Height of beds:
There does not appear to be any specific guideline on bed height. It's up to the designer and hence this probably explains the variety that people have noted. The ADA does require certain spacing around the bed to provide a clear path.
Re: Roll-in showers:
Hotels with greater than 50 rooms must have a few rooms with roll-in showers. Roughly 1% of the rooms are roll-in and 2% to 4% must have an accessible shower (grab bars, etc.). The ADA guidelines allow a lip-less roll-in shower to fit in the same space as a bathtub without requiring additional space for turning.
Re: ...curious to know if DVC/WDW builds them wrong out of ignorance or are they just following ADA guidelines:
The ADA guidelines are specific but do not cover every detail of the design of a space. The guidelines cover most public spaces and uses. It is a pretty broad area to try and legislate. Some of the guidelines are requirements, some are recommendations, and they are specified to be minimums. The majority of the guidelines deal with accessibility and maneuvering. There is no standard blueprint that must be followed. Just simple statements for a given turning radius, distance from a grab bar, ratio of special facilities to standard facilities, loudness of audible alarms, etc. The entire design process is left to the designer/architect to determine for the given environment.
Also remember the ADA guidelines have not been around for that long, so many buildings were built prior to the new construction requirements.
Hope this info helps answer some of the questions.
Troy