Quicktime (and other related apple software) not reproducing some avi files
Unfortunately this has a simple answer. Quicktime will not play any type of video file, some types it just fails on.

You used to be able to buy the MPEG-2 Codec from Apple as an add-on for Quicktime to allow you to play more kinds of video files but I don't believe they sell it any more.

You have already found the solution to playback though: VLC.

Flip4Mac used to be a Microsoft solution for playback of WMV video files but they don't support it anymore. Instead Telestream has the software, which you can purchase on their website.

And any video that Quicktime chokes on will likely also fail on any Apple apps like Keynote. You will have to convert it to another format before inserting it into a keynote presentation. 

And if your wallet is feeling a little skinny these days FFMPEG is an open source video converter and iFFmpeg is a Mac front end for it.