Are you sure? I'd understood the first few seasons were done in 4x3 and actual 16x9 episodes weren't done up until some time after the series moved its cable run to SciFiChannel.
That was supposed to be one of the pluses of the new release. It being in widescreen.
The first DVD boxed set is in widescreen?
Every episode was shot for 16:9 and are presented as such on the DVDs. However, I believe season one and possibly season two were shot on 16mm which means they may not look so great for any potential Blu-Ray release.
You may be confusing this with shooting specifically for HD which didn't start on SG-1 until either "Lockdown" or "Zero Hour" in season eight (I can't quite remember which). Atlantis was shot with HD cameras from day one.
The use of 30mm film cameras from season 3 of SG-1 onwards does not preclude the possibility of a Blu-Ray release although the CGI special effects were prepared for standard definition television broadcast, not HD. Most likely someone would have to pay to have those redone.