You are talking sense. However... Lego does a terrible job managing inventory. We can see by their summer catalog they expected the SSD to last well into, well, the summer. Oops. Anyway, their minifig packs don't generally combo with the other sets. I think they're in their own little world, like the "Planet" sets. The DS Troopers are awesome, but I think they're meant more to be the "poor man's DS", as opposed to a complement to 10188. For one thing, they come with their own gun. 10188 has plenty of guns already (turbolasers and super duper mega planet destroying laser). If anything, I could imagine Lego seeing the Troopers as a sort of replacement for 10188.
Anyway, here's a strong reason for 10188 to go: Lego wants to raise prices. Look at 10221 vs. 10030: very similar piece count, radically different prices. 10188 has a similar price/weight ratio as GE. For a licensed set, this is very unusual. I'm sure Lego would like a 3800-piece SW set to retail at $499, not $399. But Lego almost never (AS maybe the only exception?) raises prices on a set after it's released. By Lego tradition, the only way to stop selling the DS at 2008 prices and take into account dollar devaluation since then is to retire the set. In a few years, maybe we'll see a new, slightly modified, much more expensive DS. But it's time for 10188 to go, and every sign, except for the prediction of one anonymous mystery man, says it is on its way out.