You having a good experience doesn't negate that they can, for whatever reason they choose, not honour a warranty in an unlocked phone. If they do that you have zero recourse. Zero.
Ok, so first hand experience doesn't count. :-) I guess I got 'lucky'.
The disclaimer doesn't negate a warranty. It says 'may'. I could give countless examples why a disclaimer would be used and makes sense. It's been discussed before, so there isn't any point in distracting further from the topic.
If you unlock your phone via HTCDev.com you should consider your warranty voided for all intents and purposes, if that doesn't sit well with you then don't do it. I think this is the only correct way to council people about it. If you are still prepared to do it, and you do have a warranty issue, then naturally you should still approach them to see whether they will fix it.
Ok but I'd argue that the same applies with any manufacturer.
Unless you can point to a manufacturer providing a specific guarantee (that their device will be covered under warranty in all circumstances with custom roms/software), then I can't see that this is anything to shake a stick at with HTC.
I'm just saying, be reasonable. HTC are not out to prevent people from unlocking the phone. They allow it. They repair the phone if it breaks.
Perhaps in some weird situation where someone uses a custom rom, overclocks their cpu til it fries, then claims warranty on repair, then perhaps it could be rejected for repair. I'd expect it would have to be demonstrable for the warranty claim to be rejected. In my experience, warranty claims that are rejected are explicit in why the rejection took place.
Don't kid yourself and think Samsung wouldn't do the same. I don't know if they have a disclaimer, but no explicit disclaimer doesn't mean anything either unless there is an explicit guarantee.