CKEditor buttons look different on different sites.

I downloaded the following version of ckeditor: http://download.cksource.com/CKEditor/CKEditor/CKEditor%204.1/ckeditor_4...

And uploaded it to 4 different drupal sites (all drupal 7). The buttons available on each site look different, and on one of the sites the editor doesn't display at all. Why might this be?

Find and replace separate buttons for example are only displayed in one site. In the other site, a replace button is displayed but the icon is very different (a/b).

I've got the Full text format selected on all sites by the way