It is actually quite common for manufacturers for advertise LCD's with only 6-bit color depth as "16.2 million colors". The actual number of colors in these is 262,144, but with varying the shades of nearby pixels (the method called dithering), human eye can be tricked enough to perceive more colors than 6-bit color depth can achieve.

Personally ... I have used and owned several 6-bit LCD's (typically with fast response times and cheap price tags; telltale signs of weak color depth) and 8-bit LCDs too. I now own a 24" Samsung with 8-bit color depth. The difference to 6-bit panels is just stunning. Eventhough the LCD with 8-bit color depth and better panel  cost me almost 1500 USD, I would not want to go back to lower color depths any more.  In my opinion there is a huge difference between these monitor types, but then again I actually care about what I see on the screen.