This warning applies to those who play in CBS Sportsline leagues.  Strasburg is eligible to be picked up as a free agent on Sportsline in NL Only leagues but not in AL Only leagues.  In fact, Sportsline already has Strasburg's "affiliated" MLB team as the Nationals.  

There is a small chance (signing issues) that Strasburg falls to the Mariners as the second pick.  So what if that happens?  If Sportsline handles things as they have in the past it means all those teams in NL Only leagues who picked up Strasburg will have an ineligible player.  This may not seem like a big issue to some but it can be an issue to others.  Sportsline traditionally has only a few spots available for bench players- although this may not apply quite so much to those who run their commissioner service.  

The oddity is that Sportsline seems to be indicating Strasburg will be eligible nomatter which MLB team drafts him.  This may not be the case at all.  A couple years ago Roger Clemens signed with the Astros a year after being with the Yankees.  Clemens was eligible in AL Only leagues and able to be drafted in those leagues.  It was later he decided to sign with the Astros.  But upon signing with the Astros Clemens was no longer eligible in AL Only leagues.  I had carried Clemens on my roster for several weeks, just waiting for him to be activated.  But it was all for nothing.

If you pick up Strasburg and he is drafted by an American League team and if  Sportsline decides he is no longer eligible in NL Only Leagues you have no right to complain.  But a lot of that will depend on Sportsline and how they decide their rules.