And perhaps Freebase: http://www.freebase.com/

I think they supplement each other. Wikipedia is a great place to go explanatory material; statistics are a part of that but if you are really interested in the numbers behind something you'll probably follow up the citations. Alpha looks to have great potential as a tool for statistical discovery and analysis, but I rather doubt it auto-generate tutorials on what data mean or why they matter.

It would be nice if Wikipedia can improve the quality of its articles by linking to Alpha; I hope Wolfram research won't exert a propriety attitude to its search results, but will make them available with something like a creative commons license to the extent that the original sources are in the public domain.

Quoting Wikipedia is not respectable in an academic context because you are not quoting a primary source, or even a secondary source. You are typically quoting a tertiary or quaternary source. If the article is properly cited, however, it is not difficult to simply quote the original citation.