They do come with on-site warranty - as in if you have a problem and you phone them up about it they should be at your door in a day or two with a replacement monitor. They wither take away the faulty monitor there and then or collect it the next day.
As for the pixel policy, with their Ultrasharp range monitors if you have single bright/hot pixel then they will replace the monitor. However, if you have dead pixels then there is a tolerance level for this - so depending on the number, their location and concentration they may not replace the monitor because of dead pixels. That said, it is always worth calling them up as it seems the tech support guys have a bit of leeway with authorizing replacements (ie make a fuss and see if they placate you).