Are the images linked or embedded? If they're linked and the author just used the originals, then you have the original source files (so I assume that's not the case or you wouldn't be asking).
Assuming they're embedded images, does he have "picture compression" turned off in PPT? If not, I'd assume he's compressing for the target size and there may be some quality loss.
I think most manipulations of size, sharpness, hue, etc will result in some loss of data, but if the images have not been manipulated much and you can get a resolution that is larger than what you'll need on the web pages, I would say to drop it and leave well enough alone. If he doesn't like the image quality, tell him you used what you gave him.