Each park has different policies about closing rides -- Cedar Point actually lets the ride ops handle a lot of closures themselves, without haveing to wait for maintenance. If the ride "sets up" because of a problem loading/unloading guests, or illness, then the ride ops have to call the office and let them know but maintenance does not have to come check the ride and management doesn't either. The ride ops clear the problem and reopen the ride, usually in less than 5 minutes. Yes, there are a large number of mechanics on duty, and they do have smaller areas to cover letting them get to the rides more quickly if need be.
Another reason CP may not seem so bad with ride closures with some other parks is that if one coaster is closed, you still have 13 more to choose from!
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Po!nt of View: A different look at Roller Coasters.
http://www.crosswinds.net/~justmayntz/thrills/index.html