I think this is the 2003 study, although the 2004 study was probably done using a similar methodology.
Oh crap, I completetly overlooked the dates on the summary...
My biggest qualm with this (and most) surveys is that there is no indication of how the products are being used, only that the respondee is aware that the product is "in use" in their organization.
For example, if an organization uses MQ Series (now WebSphere MQ) for connectivity, are they using the app server or not?
This is a common allegation from BEA (which does not mean that it is false). WebSphere brand is huge and product branded with it usually do not use the app server at all. Although worst offenders (e.g. CICS Transaction Server) don't have "WebSphere" in the name, but are only grouped under this umbrella.
Similar thing might be going on with Oracle app server as well, as it is a prerequisite for quite some applications from Oracle Application Suite. Caveat from the next paragraph still applies, though.
Also, I suspect that almost all J2EE developers have used JBoss at some point, either for learning or to try what you get for $0.
I'm also surprised that SAP doesn't have a larger share of the "App Server" market than JRun, given the fact that more and more of SAP's installed base is being required to use it, at least for very specific tasks.
This is probably just a (branding) perception artifact. Remember, the criterion is "aware that the product is "in use" in their organization". From my experience SAP is regarded as a big monolithic chunk by those that don't have to use it. And most people (SAP administrators *and* J2EE developers) are not thrilled by having something deployed on it...