No, not really it all depends on what is in it.
I have produced two multi-touch video books and the samples are also large due to the amount of video content within the iBooks samples. If it gives people a good sense of what the book is about it is a good idea. The only downside is that the larger the sample size, the longer it takes for people to download it.
I agree to a point about being put off by the download file size. Not all countries have fast or low priced broadband connections.
However, all videos can be edited and a shorter version used in the sample book. You can also add a note to advise those downloading the sample that the purchased book contains the full version of the videos.