The OS is one step below the latest, and they have said it will be updated soon. "One year old" sounds like what Apple were saying about the S4 before launch
. No, not worried there - though TBH I'll root and go custom pretty quickly with any phone I buy, so am more concerned myself with the size of the developer base than the manufacturer's update record.
I'm not worried about warranties not being honoured, and in the EU those are 2 year warranties. And how many phones don't have some teething troubles in the first batches? The best selling android of last year still has problems with some SD cards and the international version had (and for many, still has) a bug which can cause the phone to hard brick ("sudden death syndrome"), and there are threads here about some service centres still failing to handle this properly. My point here is not bashing any brand or model (I like the S3 a lot), but rather that a nervous customer could find reasons for avoiding any manufacturer.
Yes, I'd be happier if HTC's state was better, and indeed think it will be healthier for all friends of android if it improves. But I'm going to make my choice on the merits of the device and how well I feel it suits me.