That type of doublespend is trivial to detect. Merchant waits 10 seconds and merchant (or payment processor) has a dozen listnening nodes geolocated around the world. Within the 10 seconds either merchants tx propogates the entire network or your double spend hits one of the listening nodes. If double spend is detected POS terminal reports "payment declined" and cashier asks you for payment in another method.
Well that is a good point, although I'm not aware of any feature like this in standard bitcoin core to report double spend transactions (but I saw some discussions proposing that, were any implemented??), so they would have to have their own customized node software to report the double spend attempt, but that probably wouldn't be too hard since much of it is open source. You are correct that 3rd party services can and probably will implement this as a feature (and perhaps they are doing this already). In fact I'm sort of surprised I haven't heard of it already being offered.
What I have seen is the green address technique, which can use 2 of 2 multi-sig transactions and a trusted 3rd party for instant 0-conf payments with double spend protection (assuming 3rd party is trust worthy).
But why isn't everyone adopting your proposed technique? It really isn't being done yet is it? Or if it is, post links to services offering this.
References:
https://github.com/bitcoin/bitcoin/issues/1034http://sourceforge.net/p/bitcoin/mailman/bitcoin-development/thread/519AC3A8.1020306%40quinnharris.me/#msg30873782