why are you using Web Installation at all?
Quite simple... Web spider search engines will find embedded EXE links in HTML pages and part of the spidering process, download the EXE in the process. This can lead to dozens to hundreds of unnecessary downloads of the EXE. If I have a 400MB EXE linked to a HTML page, then I run the risk of this useless bandwidth occurring. But if I use Web Deploy, and have only a 25K EXE stub, then the bandwidth usage is minimized since the search engine spider is highly unlikely to execute the downloaded stub.