We "or" DTR and RTS so that if either signal is high (or both) you can get some juice from it. You need to make sure the PC enables hardware flow control.

I suppose you might have some failures, so if your business model can cope with that then you are OK. We have some el cheapo products that do this and the product return rate is surprisingly low. Certainly on our flagship products we use more reliable methods (supply a wall wart or use USB). Problem is, many people seem to want the cheapest option (I'm talking about the consumer here), so if you're only willing to pay for crap, that's exactly what you'll get. Take a trip to WalMart or Target. Wall to wall crap. But I digress ... ;-)