Ubuntu, being a hunk of an OS, is not giving out Ads! I mean, See Microsoft for instance, Whichever Blogs or Websites you Visit you get a Nice girl holding a boquet of flowers and saying Windows 7, Beauty and Brain.
In My country, India, Ubuntu is so unknown to Non-Geek people that they wonder if it is some Alien Product, Why doesnt Canonical think of it? Doesnt an Ad in some Newspaper Exponentially increase its users?
there are ads. I'll admit they are few and far between. Techinically we haven't had a flagship release as yet. 12.04 should be that release. I think we'll be seeing more ads after April comes.
Money talks !
AFAIK, Ubuntu started with a funding of $10m and obviously Canonical won't spend more on ads.
You're mentioning Microsoft:
Advertising expense was $1.9 billion, $1.6 billion, and $1.4 billion in fiscal years 2011, 2010, and 2009, respectively.
Advertising expense was $1.2 billion, $1.3 billion, and $1.2 billion in fiscal years 2008, 2007, and 2006, respectively.
Sources: http://www.sec.gov/Archives/edgar/data/789019/000119312511200680/d10k.htm
http://www.sec.gov/Archives/edgar/data/789019/000119312508162768/d10k.htm
Actually, Ubuntu does have a hell of a market share relative to how much is spent on ads.
Ubuntu relies on mouth-to-mouth marketing + image marketing instead of adds, which seems one of the most effective ways of marketing. But some adds will improve marketing a lot.
