The reason is that HTML words are the American English, not UK.
For example <center> rather than <centre>, <bgcolor> rather than <bgcolour>. So make sure you spell it the American way, if unsure, check out http://www2.gsu.edu/~wwwesl/egw/jones/differences.htm
for all the comparisions - press CTRL and F together to search the page.
And remember in the future, we DO have a Web Design / Reviews / Advertising board, and that is not the General Lounge!
Hope that helps, remember to thank me because if you don't it's rude