I think the biggest problem with wolframalpha.com (besides its hard and long name) is functionality discovery. How am I supposed to know it's possible to measure "plane overheads", even if I am on their site?
That's interesting to see the related searches between the two. Github users, unsurprisingly, also like Node, MongoDB, etc., whereas Wolfram Alpha users play Minecraft and read webcomics (also popular among Github users). In other words, Wolfram Alpha seems to be commonly used by students, presumably in math, physics, and engineering.
Anyhow, from the website usage, it looks like it never took off: http://trends.google.com/websites?q=wolframalpha.com&geo...