Lol, somewhere a Rainforest breathes a sigh of relief.
They did the big reissue in '99 of the DC, U1, U2, U3, Convertible, & Longhorns. Then they added the Hodad & Mod line in somewhere after that ('00-01). Then I think the company that had/has the right to produce Danos changed hands/bankrupted/something. The next time new reissues showed up was '06, with the Longhorn with the adjustable saddle bridge and then the Dano Pro, and Dano '59 guitars the next year. Now they're issuing the Dano '63.
My guess is they're doing limited runs to increase the popularity or demand. I dunno. =)
I'm not as big a fan of the newer ('06-) reissues, not because of the hardware changes, but the lack of matching neck and headstock paintjob. I think it made the newer reissues less reminiscent of their older brethren (Minus the Dano 63', since they were shooting for the Silvertone vibe).
Also, for anyone interested,
http://www.danguitars.com is a good site that has a lot of history of the Danelectro/Silvertone company and has a lot of great pics. Plus they buy and resale the Reissues and parts to upgrade/repair them.