It has become more and more common for web sites to implement some degree of personalization, regional targeting, or other forms of individualization in the way web pages are served to individual users.
In its most simple form it can be a program on the Server that checks what browser people are using and serves up a specially tailored version for that browser. The same kind of program can also be used to check if people have specific plug-ins installed so that they get a version of the web site they can read.
A more advanced use would be to check what country the user is coming from to serve a local version. Some portals and search engines have been doing that and many other cross-national web sites do it. There are many legitimate reasons to do so including business strategies, marketing, and legal issues with products that are only allowed in certain countries.
The same techniques can also be used to serve different content to search engine spiders and normal human visitors. These techniques are usually referred to as 'Cloaking'.
In most cases search engines do not like the use of 'cloaking'. Your pages can be banned if you use cloaking! Thus, do not use cloaking unless you have a very good reason to do so.