12ms response time... is this rather slow for a high cost display?

I was waiting to buy the new 27" display but now that it has been arrived at a cost of £899 in the UK I am looking at cheaper alternatives, accepting that cheaper will probably mean lower spec. I am surprised to find that many much lower priced displays from manufacturers such as LG, HP, and Samsung appear to have faster response times, for instance 2ms or 5ms, whereas the Apple display's response time is listed as being 12ms. I think I am correct in thinking that a lower response time means that fast action video looks better on screen, but this doesn't seem to make sense that such an expensive and high quality display as Apple's would be slower, so am I misunderstanding something here?
What are the most important figures to take account of when looking at the spec of a good display?