It's one of the challenges that this portion of the industry faces. There isn't one tool that is a "catch-all" for malware products.
Why is that?
Well, as Stu stated, one of the reasons for this is that many of these applications are driven by a very small market base at present. Despite the fact that malware has existed for quite sometime, the means to fight it (and properly identify it) is still in its early phases, I use that term relatively mind you.
In addition to this, each spyware tool has its own way of rating what applications, registry entries, and files should be removed. Some applications may have a specific software package listed as a "to be deleted" and another may not. This is what, recently, caused such an uproar against Lavasoft. They were delisting products from their malware database due to their rating system.
Lastly, this is a very dynamic arena. Unlike virus', the majority of malware comes with a profit attached to it. It gives a great incentive for its creators to continually evolve the applications that they write and how they are installed to your system.
For the above reasons, and probably many more that I'm unaware of, there is no current "catch-all" application. It is why so many people will recommend, myself included, two or more applications for spyware removal and monitoring.