The top 3 also have much cheaper models than Apple.. which can contribute to their higher sale spots. Not many people are willing to sell out $1k for a computer, especially internationally. In Brazil, a MBP costs about $3k. DOLLARS. Not many people can afford that..
That's the problem. I see Dell, Hp, etc PC's at walmart with lower specs selling for $400-$500. You get what you pay for. Same for PC's at Bestbuy. The higher spec ones are in the $900 to $1000 range. I think if Apple was to move the price of the current white macbook to $500 more people would buy apple. Then cut the price of all other machines buy $100-$200.
I think also why you are not seeing much macs in the enterprise still:
1. Microsoft exchange and outlook. outlook combines your address book, calendar, mail, and tasks/todos without having 2 or more apps open.
2. Microsoft SQL Server. This has better ODBC connections than other databases when connecting to access, excel, etc. Plus, while I have not verified; other than a source who programs databases in Filemaker and SQL server... Filemaker is elegant, but cannot handle 1000's of transactions per minute like SQL server can. Thus not good for banking or healthcare.
3. iWork still a light application and Office is still the standard.
4. While I have not tried it, I heard Citrix is atrocious on non-windows platforms
5. MS keeps copying Apple features, so fewer people feel the urge to switch.
6. Also, you would be surprised that more and more big corporations are actually using Linux on their servers. Recently in the news, highlighting top North Carolina companies who have not been effected buy the recession; Redhat was focussed upon. They have grown tremendously and now only sell their OS plus applications to enterprise corporations. What makes them strong? RedHat gives 10 years of support for any version for free.
7. Mac pro is rediculous in terms of pricing. However, now that it is rebranded as a server, makes the price ok.
8. While Mac OS X is unix based (Free BSD); running Linux or unix applications on it is 25-50% successful at best. That stinks for open source only users.
As for the iPad, let's just say thanks to the app store - I use mine more than just a net book, toy, entertainment, etc. But I also still rely on my 2008 macbook for some heavy weight applications.