Why don't Warehouse 13, Eureka, Stargate, Sanctuary, and Battlestar Galactica exist in the same story universe? They so easily could.
One of the most exciting bits of the first Iron Man flick was when Samuel L. Jackson's Nick Fury showed up, talking about the Avengers. The idea that a series of movies could do what comics have for so long — exist in a shared universe, each installment forming a piece of a whole — was exhilarating. TV flirts with it: there have been in-franchise crossovers since forever — Spock appearing on The Next Generation; the varied CSIs mingling together to watch Caruso do his sunglasses trick.
Lost has been a part of a bit of that: One of Chuck's flashes revealed that Oceanic Flight 815 was hit by a surface-to-air missile, the DHARMA logo popped briefly in the beginning of Cloverfield, and sharp-eyed viewers caught an Oceanic billboard in the background on FlashForward. That's the kind of thing that tickles the geek pleasure center; Syfy has a unique opportunity to extend that throughout their whole scripted lineup. A whole network tied together by singularity of content...why don't they?
Why couldn't Warehouse 13's Myka and Pete go on the hunt for an artifact squirreled away in the basement of Global Dynamics in Eureka? Why couldn't Battlestar Galactica and Caprica exist in the distant past of the present shared by Sanctuary? Why couldn't the crew of Stargate Universe stumble upon a wonderfully evolved Cylon homeworld somewhere in the cosmos?
You don't have to hammer people over the head with it, but how cool would it be if Syfy did one massive crossover event that brought all these people together to fight a common threat? It's the only network that could pull off a shared universe — I wish they'd give it a shot.