Noggin, yes i am inclined to agree with you.
Honest Frank.....a little bit offensive i think. Instructors are underpaid as it is. If you were an instructor how would you feel about sending 2 of your students off on solo flights and not earning any money for the rest of the day?
If a student is flying solo he is entitled to the guidance (supervision?) of an instructor. This forms part of his training and part of the ppl syllabus.
I would suggest that the worst scenario based on your thoughts might be instructors doing more dual flying than necessary in order to earn money.
Think about it.
JWF