The strength of Mathematica, and hence W|A, is not the CAS functionality - there are many other packages that do math - but rather the well-designed programming language.
Everything in mathematica is a computable expression, and every expression has a uniform symbolic structure. Contrast this with the toolkits and such in Matlab/Maple that put functionality in a separate window --- new capabilities must be 'tacked on' rather than fully integrated into the system.
Here is a plot of the growth of the number of functions in Mathematica over the years:
Along with an excerpt from a blog post by Stephen Wolfram upon the release of the latest version of Mathematica November 2008:
Watching our development process from the inside, I’ve definitely had the feeling in the past few years that we’ve been entering a new regime of growth. That everything we’ve integrated into Mathematica is interacting to let us somehow build almost exponentially more.
And the plot above suggests that something like that is really happening.
But what’s perhaps most striking is that even as the number of functions and the breadth of functionality have been growing so dramatically, we’ve succeeded in maintaining the unity of Mathematica—and of making sure that every piece of the system fits together in a coherent way.
That’s not been easy, of course. It’s the result of our long-term company culture and of a lot of systems that we’ve built up over the course of more than 20 years. (As well as thousands of hours of personal work by me.)
It’s very satisfying, though. Because it means that the things we so carefully built five, ten, twenty years ago are still there today, making possible our new achievements.
The strengh of Mathematica for a project like W|A is the uniformity of its design, the standard structure of expressions. This allows for the code to be extremely concise, because there is a minimum of special cases, and one can write functions that are very general and highly automated.
It has been said that W|A is already running over 5 million lines of Mathematica code: if it were even possible to write something like W|A in C++, in my experience it would be larger by a factor of 10, over 50 million lines.
Google uses python, C++, and java, and each function in
http://www.google.com/intl/en/help/features.html is seemingly coded as a special case --- just like adding new toolkits to the next version of Matlab or Maple. It's unlikely that we will ever see Google's weather data be computable against its sports data, but W|A, although it does not yet have sports data, is designed to do this sort of thing.
As Phrak discovered WRI is privately held, and I will be surprised if and when they ever go public --- somethings seem to matter more to Stephen Wolfram than money. Based on what I know about the man, I will be surprised if a big company like Google or MS is ever able to get a piece of Mathematica just by throwing money around, at least during Stephen's lifetime, but that's what everyone says before the cash presses start rolling
Wolfram emphasized from the beginning that private information would not be a part of W|A, and although I find in strange that the engine will not discuss it's creators, this is keeping with that general policy.
For those of you who like 'web 2.0' there is now a Wolfram|Alpha community website which allows posters to provide suggestions, and potentially data, etc:
http://community.wolframalpha.com/