Why Wikipedia result is coming in most of the cases in Google SERP

All of us have seen that Wikipedia result is coming on the top whenever you are searching for some thing however competitive the key phrase is. Wikipedia.org is a multilingual, Web-based, free content encyclopedia project. Wikipedia is written collaboratively by volunteers from all around the world. Since its creation in 2001, there are 2,428,787 articles in English read more about Wikipedia at http://en.wikipedia.org/wiki/Wikipedia:About

The possible reason for their top position is
1. Is there any tie up between Google and wiki and Google has taken the responsibility to promote wiki?
2. Are they well optimized their page for SEO?

Content is the king, and wiki is on the head of the content. Wiki has well reached with semantically related content; they have good number back link from its own domain. Suppose you are searching for “hotel” in wiki, probably you will get a url in the top of serp like “en.wikipedia.org/wiki/Hotel”. It seems they are naturally optimized for SEO as they have hotel in their url. Wikipedia's articles provide links to guide the user to related pages with additional information. Also it has a good number of back links from pages like “en.wikipedia.org/wiki/Hotel_Chelsea”. These are the quality natural, content rich back links, which Google considers the most.
One of the interesting thing I found is if I am going for a single phrase word, I found wiki at the top but if I am adding another word to it or going for long term key phrase it’s coming down. Still not clear about the concept of Google. if any one having any additions to the above please comment it here, suggestions, feedbacks all are well come…… J

How Google defines IP delivery, geolocation, and cloaking

Geolocation: Serving targeted/different content to users based on their location. As a webmaster, you may be able to determine a user's location from preferences you've stored in their cookie, information pertaining to their login, or their IP address. For example, if your site is about baseball, you may use geolocation techniques to highlight the Yankees to your users in New York.

The key is to treat Googlebot as you would a typical user from a similar location, IP range, etc. (i.e. don't treat Googlebot as if it came from its own separate country—that's cloaking).

IP delivery: Serving targeted/different content to users based on their IP address, often because the IP address provides geographic information. Because IP delivery can be viewed as a specific type of geolocation, similar rules apply. Googlebot should see the same content a typical user from the same IP address would see.

Cloaking: Serving different content to users than to Googlebot. This is a violation of our webmaster guidelines. If the file that Googlebot sees is not identical to the file that a typical user sees, then you're in a high-risk category. A program such as md5sum or diff can compute a hash to verify that two different files are identical.

First click free: Implementing Google News' First click free policy for your content allows you to include your premium or subscription-based content in Google's websearch index without violating our quality guidelines. You allow all users who find your page using Google search to see the full text of the document, even if they have not registered or subscribed. The user's first click to your content area is free. However, you can block the user with a login or payment request when he clicks away from that page to another section of your site.

If you're using First click free, the page displayed to users who visit from Google must be identical to the content that is shown to the Googlebot.Still have questions? See related thread at Google Webmaster Help Group.

How Google defines IP delivery, geolocation, and cloaking: