Oh it was just a guess. I know that if you take shelf exams at certain times of the year the NBME forces you to wait longer in order for statistics to be accumulated so they get a big enough sample size to see how students performed on those questions before releasing scores. Maybe they don't do that with STEP 1.
For what it's worth, a very similar message was posted last year as well. I guess it's just routine, but they sure make it sound pretty ominous.
"Most score reporting of Step 1 results occurs within four weeks of testing. However, because of necessary modifications to the test item pool, there will be a delay in reporting for some examinees testing beginning in mid-May 2011. The target date for reporting Step 1 scores for most examinees testing from May 17 through late June will be Wednesday, July 13, 2011."