[HTC One X] TheBrilliantMistake:
No it doesn't.

It says this:

It is our responsibility to caution you that not all claims resulting or caused by or from the unlocking of the bootloader may be covered under warranty.

This is where the ambiguity lies - HTC will claim bad software could result in hardware damage (true). The issue is, DID bad software cause it?

In many cases - e.g. broken power button, loose USB connection, it's clearly not caused by software. Heat damage / flash damage can be trickier - a rogue app that writes garbage to flash a few millions times could basically wear out your flash (for instance).

Still, the fact remains - HTC does NOT say your warranty is invalid, it simply suggests it could be compromised.

When it comes to consumer law in the UK (Sale of Goods Act) - any issue with your device is the sole responsibility of the retailer (whoever you bought it from). If you have an issue, you should always go back to the place of purchase with your claim. NEVER be fobbed off with 'it's a manufacturer warranty'. It's the job of the retailer to fix your issue (even if they themselves have to deal with the manufacturer).

There is a 'technical' element of the law that states a product claim can be made up to 6 years after purchase.... but this is also dependent upon the interpretation of 'expected lifetime' of a product, and it MUST be a proven manufacturer defect - an example of this would be a car with a 3 year 'warranty' - but the engine explodes after 5 years due to a known defect. You'd be entitled to a repair for free under the law because you would reasonably expect an engine to last longer than 5 years.

It should also be noted that the onus on proof is NOT with the manufacturer or retailer. The consumer (YOU) have to be able to prove there's a manufacturing defect. This can be extremely problematic to prove, but if HTC ever state 'we have an LCD failure issue' and your LCD fails, having an unlocked bootloader should not affect your statutory rights.

IF you can be bothered, then you can always take a retailer to the small claims court (as others have suggested) - but all the while you might be without your phone. If your claim in reasonable, the chances are you'll win. The 'judge' is a layperson, and it's all very informal and usually take about an hour to resolve in court. The general principle is 'what would a reasonable man in the street think was fair?' - that's the outcome you'll get.

The law in each country differs of course but for most of the EU it's similar.

In the past manufacturers have tried to bully consumers - the best example of this was when car manufacturers tried to insist you have your car serviced by a main dealer in order to not void your warranty. This was judged illegal and you're now entitled to have your car serviced by independent companies too.

Summary -

1) When a device goes wrong - it is the responsibility of the RETAILER to correct the problem. The contract you enter into when you buy a phone is between YOU (the consumer) and the seller (the RETAILER).

2) Unlocked bootloaders and custom roms do NOT necessarily invalidate your warranty (and HTC do not claim it does).

3) Unlocked bootloaders and custom roms MAY damage your device and if they do, your warranty is void for that damage (but not for non related damage)

4) Unlocked bootloaders and custom roms MAY give the retailer an excuse to challenge your warranty - which then results in 'hassle' trying to get your repair.