The battery on my HTC Desire was still good for a full day's usage with something left in the tank after 3 years - and I charged it every day.
I don't think it should be too much of a concern. Plus, if you're in Europe, you have a two year warranty which - presumably - would cover the battery as it is non-swappable.
Lots of phone manufacturers have moved to non-swappable batteries. Given they all source their batteries from the same battery manufacturers, I see no reason why HTC should be any worse than anyone else.