Depends. If you wanted them to run the disc while you waited, then yes. If you were looking to obtain a disc for your own use, then no. Genius Bar doesn't stock discs for customers, ... you have to call AppleCare for that.As I stated earlier, I pretty much went in there knowing what I wanted, the System Diagnostic Disc. And until June 16, 2009, they probably would have been able to help me.
The basic phone menu of all of the US stores is the same. Press 5 to talk to someone in the store. You are correct that you can't phone up and ask a lengthy technical question. You could, however, phone up and say "I have an old PowerMac G5 that's having problems and want to know if I made a Genius Bar appointment, could they get me a diagnostic disc". Whoever answered the phone would put you on old, stick their head in the Genius Room, ask the question to one of the Geniuses working the bench, and relay the answer back to you. You don't get to talk to the Genius, but you do get the answer you needed.No, you can't. They prompts on the automated line state that in order to speak to a "genius", you need to get an appointment. I'm not sure which store you shop at but the Farmington, CT store, they're a little short on that kind of service.
I don't disagree that it would be cool if the online Concierge system could flag you in advance if you had vintage equipment. Apple makes regular updates to the Concierge system. The more folks in your situation that make your dissatisfaction known via a method that Apple tracks (i.e. fill out the email survey if you received it, or simply call the store and talk to a manger), the more likely your suggestion is to be implemented.