Burnout Paradise addons for PC
None of the addons, except the motorcycles, were ever published for PC.
This answer used to have a link to an EA statement that no add-ons will appear for PC, but the link expired.
The list of game-changing content released to Burnout Paradise is available at this wiki:
http://burnout.wikia.com/wiki/Game_Changing_Content
In that page, there is a table that shows what kind of content is not available on PC.
Also, the "Burnout Paradise: The Ultimate Box" includes the Bikes addon (and maybe one or two updates too), but it has a bug that won't let you change the colors of the extra unlocked bikes. This is a known bug and was fixed in Big Surf Island update. However, since Criterion Games won't bring that update to PC, we're stuck with that bug forever. :-(
I'd add a link to the actual bug report, but Criterion Games Bugzilla has changed the address and now requires login.
Although the console version has more updates and more content, the PC version is still good. On the other hand, given the choice, it's probably better to pick the console version.