I don't do HTML export, but what happens if you DON'T use the preserve appearance option?
Then you just get the image at its original size (as if you never formatted it.)
Perhaps I misunderstood. I thought you wanted to preserve the image dimensions.
Are you scaling the images up in ID?
Sorry, just realized that the problem was exporting it at a res of 150ppi. You can export a png from Illustrator and give it any res you want but it retains its pixel dimensions. Obviously not the case with ID CS5.5.
Thanks for helping.