Well, in that example there is no difference, it's just part of a push away from using html attributes for style and towards css.

IF I understand right the current movement is towards having the HTML (to be replaced by XML) describing only the actual content. Then how it is represented on the screen would be described in the css. This way if you only need one data file when using the same content in different ways ex: display on a computer monitor/cell phone/pda/import it into a database, etc....

Of course this only applies when you use an external stylesheet, not when you have the style embedded right in to the tag. I suspect this will one day be depricated as well and is only allowable now to make it easier for people to transition from the old way to the new.