mislav:It's PADI. I've witnessed this behavior and mentality on several occasions, including twice on myself, back in the days of my first dives.
The reasoning is along the lines - the customers should relax and enjoy the sightseeing and not focus on their buoyancy.
No. The answer to what the reasoning is lies in understanding what the "Dive Today Philosophy" is. The idea is to get people in the water, get them interested and keep them interested. By arranging things the way they have students can get training credit for that resort try-it dive...and so already being part way to certification serves as incentive for them to complete the program. That's all good from a marketing standpoint. From in instructional or even a safety standpoint, I think it's a total nightmare.