Employers aren't just using degrees as filters. In software, there is a wide variety of disciplines (engineering, administration) and a large quantity of tools with which one can be skilled. While the former presents legitimate differences in skills, the latter can often be chosen arbitrarily, by vendor or by the desired outcome of the product. Not having experience with a particular tool doesn't mean that one isn't qualified to do the work, but ti's very easy for an employer to narrow the field by requiring so many years with a particular tool—most of which didn't even exist 10 years ago,

This goes back to the idea that there is great demand for diplomas but less demand for education. Employers ultimately have a job that needs to be done. The skills needed to perform that job are abstract and sometimes hard to define. Degrees and years of experience with specific tools provide tangible, but poor, means of evaluating the skill needed. In today's economy, so many positions have large numbers of applicants. Applying these tangible filters makes the process manageable but really works to the detriment not just of the qualified worker but also the employer. (How many stories do we hear of hiring people with high degrees or inflated resumes who talked a good story but were incompetent or had character issues.)