This is something that has been the norm since these HDTVs started selling like hotcakes. The end user has to either live with sub-par sound, or learn how to easily utilize external speakers (which are not expensive and improve the situation enormously). We can recommend something if you ask.
Also, keep in mind the larger HDTV manufacturers do have warranties that cover dead pixels, etc. You can also extend such warranties by purchasing from specific retailers (such as Costco), using specific credit cards (American Express still offers extended warranties at no charge), and also by purchasing third party extended coverage (Squaretrade, etc.). This topic has been asked/answered here previously, so it wouldn't hurt to search back in some of the older threads.
Just keep in mind there's no guarantee that any of these products will last as long as you need them to. This is what setting money aside for emergencies is for.
Honestly though, you are looking at at least $2500+ for quality HDTVs in that size range. What is your working budget so we could suggest something specific?
cheers