are you happy now?
Irrelevant. I don't care.
are we safer now?
Irrelevant. This is a regulatory issue.
"technicians" screw up also.
Irrelevant. This is a regulatory issue. Focus.
I guess I can't check the oil, or read the oxygen gauge...what else?
You may be required to check the oil as part of your preflight duties, or you may be unable, depending on the aircraft. A good example is the Piaggio Avanti, which requires climbing on top of the wing, removing 15 specialty internally-threaded self-locking screws, remove a cannon plug and a panel, and then remove the dipstick. This is a procedure involving complex disassembly and reassembly, and for an operator under part 135, requires specific training and an authoriation.
You may be able to check your oxygen gauge (let's hope you can...you can, can't you?), but not service, refill, purge, or otherwise maintain your oxygen system.
You may see a requirement to check your tire pressure on your preflight checklist, but per recent legal interpretations, may not be able to do so as you're not qualified. Again, this may require the participation of a certificated mechanic or other authorized individual.