
All three were invited to participate along with 61 other participants. The key number to know is 15 and why that’s important. Of the 65 invitees, 15 of them which were determined by a secret NBA ballot with results released Sunday for the Monday morning combine are designated “skills, strength, agility and medical testing only” – that’s insider talk for FIRST ROUND.
The list of the 15 top draft prospects are: Joe Alexander, Jr., West Virginia; Darrell Arthur, Soph., Kansas; D.J. Augustin, Soph., Texas; Jerryd Bayless, Fr., Arizona; Michael Beasley, Fr., Kansas State; Eric Gordon, Fr., Indiana; Donte Green, Fr., Syracuse; DeAndre Jordan, Fr., Texas A&M; Brook Lopez, Soph., Stanford; Kevin Love, Fr., UCLA (pictured below); O.J. Mayo, Fr., USC; JaVale McGee, Soph., Nevada; Anthony Randolph, Fr., LSU; Derrick Rose, Fr., Memphis and Russell Westbrook, Soph., UCLA.
Add to that list a couple of European and/or Asian players and some notable absentees for various reasons and first round picks start running dry rather quickly. Not participating for various reasons are: Kansas junior Mario Chalmers, Kansas State redshirt freshman Bill

According to Andy Katz at ESPN: By far the biggest surprise is the willingness of some high-profile underclassmen to participate in the camp, notably the trio from North Carolina.
Sophomores Ellington and Lawson aren't locks for the first round, so they decided to participate and try to play their ways in. Neither has signed with an agent, and this clearly is an attempt to prove they are first-round worthy and should stay in the draft. Teammate Green also decided to play, a necessity if he wants to get into the second round and not return to school.
For more on these three: http://sports.espn.go.com/ncb/columns/story?columnist=katz_andy&id=3415036