T2i - Class 10 SD card required for stills ?

Stopped in the local Best Buy today to look at the T2i. The salesperson reminded me that I would need to use a Class 10 card with the camera. I thought maybe he was referring to only video, but he said stills would require that also. Then I thought maybe he was referring to continuous shooting, but he said shooting just a single shot needed the faster writing speed of Class 10. He said the camera is trying to write so much information for each shot that the card needs to be able to keep up. He said without a Class 10 card, the pics would not look as sharp because some of the information would be missing because the card could not write fast enough.

Is there any merit in what he is saying ? My gut feel is that this is nonsense.

Would appreciate your thoughts. Thanks !