Hey, if you define a "Chapter" as being any old group of Space Marines (like a gaggle of geese, or a murder of crows) there's really not much left to talk about.
As far as DW being akin to Special Forces, I disagree there too -- the Special Forces are still under the command of the Military. Deathwatch are not under the command of the Adeptus Astartes, the are an element of the Inquisition. I can't think of a good real-world example... maybe an elite CIA hit-team recruited from Army/Navy/etc?
Andy
Your definition of Chapter is faulty. A Space Marine Chapter has a NAME and all share the SAME geneseed as their Primarch.
And the Iquisition is is para-military, and the Marines are selected for special Inquisition missions for their tenure of service. So far sounds very much like special ops.
The Deathwatch are NOT a Chapter in the way Ultramarines or Blood Angels are. In fact, they're not even close.
But, continue to believe what you will, I won't argue anymore. At Games Day 2001, I was privvy to hearing some kid ask Gav Thorpe in the Future of 40K seminar if the Deathwatch will be getting a chapter. His response? No, they're not anything like that, and never will be.