First of all, despite the irrefutable success it has enjoyed with its 334 hours of television to-date and counting, I would still refrain from referring to the Stargate franchise as a 'vast empire'. Even in its heyday during the sixth through eighth seasons of the flagship show and the first, second, fourth and fifth seasons of the first spinoff (ratings dipped somewhat uncomfortably during the third but began to pick themselves back up later) it still never attracted more than two million viewers per week, which while enough to be considered stable on SyFy, still keeps it far from the public tongue.
This is a nitpick, I know, and I'm sorry if I'm coming off kind of silly for it. But part of it is the very real fact that I wish it really was a 'vast empire', because then we'd be getting that much more of it.
People sign onto things because they get money that way. Richard Dean Anderson still might have taken the role if he'd been offered it on a 'lesser' network than the premium cable Showtime, and most of those guest stars certainly might have. Edward James Olmos and Mary McDonell, for example, are no slouches when it comes to name recognition, and Battlestar Galactica (2003) held its entire run on SyFy.
Another thing. While Showtime is a more high-profile brand name, its status as a premium network (and indeed, its viewership was lesser in 1997-2002 than it is today) kept the series from being watched by all that many people. More people were watching the show on SyFy even when its ratings began to slide toward the end of its tenure than ever had on Showtime. What really kept SG-1 going through the gate for the first five years (besides, of course, the fact that they had a five-year contract... these things are broken if a show does badly) was the fact that its syndication ratings were winners. Enough people without a subscription to Showtime were paying advertisers on other, lower channels.
It's not like the series did poorly on Showtime, and it certainly gained a bit of a reputation for itself just from being there. But a great many more people were watching once it moved to SyFy, because a great many more people had SyFy.
Which brings us to Lindley's very valid point. 'Stargate Mondays' did a very admirable job pulling new fans into the franchise, myself included. I began watching with "Redemption, Part I", the first episode that aired on SyFy in 2002, but it was through the hard work and dedication the network showed to making sure people could get caught up from early on that a lot of us really formed connections. I was in high school then, and I was still bummed that Deep Space Nine had ended years prior.
I was a Farscape fan (and deeply dissatisfied with that same network's lack of commitment to that show soon thereafter) but Stargate SG-1 and my ability to relive the old adventures I missed four hours a week was a big, cool thing for me. As I watched the new episodes and enjoyed them, I got to know the characters' pasts on Mondays. It was something special.