9to5mac has published a vague report that claims Apple would update 4 out of 5 Macs at WWDC. We are calling this report vague even though 4 out of 5 sounds definite, because as you read the report you realize that Mark Gurman is only sure about 15-inch MacBook Pro update and rest is just assumptions without any concrete backing. These are some of the excerpts from what Mark posted:

According to sources, Apple is planning to update at least four out of their five Mac lines at the June 11 WWDC kickoff keynote. Apple’s current Mac lines are the MacBook Pro, MacBook Air, iMac, Mac mini, and Mac Pro. We are hearing that Apple will release two configurations of the redesigned 15-inch MacBook Pro, but it is unclear what will happen to the other MacBook Pro screen sizes.

Apple is working on a version of the 11 inch and 13 inch MacBook Airs with Retina Displays, and we are led to believe that these new ultra-thin notebooks will serve as the second Mac update announcement at WWDC.

The third new update will likely be a refresh to the iMac line. While it appears that a new iMac is coming at WWDC, its feature-set is thus far unclear.

Apple is also planning to refresh a fourth piece of their Mac line, and this leaves the Mac mini and the Mac Pro. We are currently unsure whether or not the Mac Pro or Mac mini will be the fourth Mac updated at the conference, but both Macs are due for a refresh, especially the Mac Pro.

Basically, this means that like everyone else 9to5mac is only sure about 15-inch MacBook Pro update. Our sources say that the two systems that are most likely to see an update at WWDC along with MacBook Pro are iMac and Mac Pro. We believe Apple will announce the Mac Pro at WWDC to let pro users know that the tower is not dead and then shipping it later this summer.