That's been my experience too. It actually saves a lot of time figuring out how to make fancy graphs and sort/filter/pivot functions--I just make nice semantic HTML with <table>s of values. The users can point Excel at my URL and it'll automagically turn it into a spreadsheet they already know how to use.
One thing I haven't figured out how to do is have a link on my page that triggers an Excel HTML import operation on the current page.