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.
The last time I've done this I just have a link that sets the content type header to something like text/excel (that's not it exactly i don't think, google for it) and on Windows at least it always worked to open the page in Excel. And if you use an HTML table, excel will just open it as a spreadsheet, including any CSS text formatting you use.
Is that what you meant, or did I answer a different question?
Unfortunately, Excel can't cope with some of the more modern authentication systems being deployed on the web, so it's no longer as easy as providing a URL that spits out an HTML table, if you have to protect sensitive data behind a login (I think it can handle HTTP-Basic, but not anything requiring redirects; this may have changed in recent versions).
ps. you should make the generated script tag do src="//r.office.microsoft.com/r/rlidExcelButton?v=1&kip=1" so the http/https issue in your FAQ goes away
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.