Yes, my problem is basically that for me a double spend would be if one of the TX had at least one confirmation, but I cant tell how common this idea is.
Small re-orgs (of 1-2 blocks) do happen fairly often but generally don't involve such "tx replacements" (although that of course *could happen*) this is why you should care about confirmations (the more valuable the tx the more you'd generally want to wait).
If I was say accepting BTC for something as valuable as a *house* then I'd probably want to wait for 100 confirmations (although maybe you think that would be "going overboard").
For a face-to-face situation involving even a few thousand dollars I would be basically happy with just a couple.