It means, rightly or wrongly they wouldn't employ someone with asthma. This, in my own opinion, is not right as they are discriminating against someone who has otherwise a valid JAA Class 1 Medical.
Then again, there are many people who are looking for jobs out there than there are jobs, so the airlines can probably be picky when it comes to medical standards.
For instance, British Airways has a more stringent medical for their pilots than that of the JAA Class 1. They state this on their website:
http://www.britishairwaysjobs.com/cc...ligibility.jsp