It was indeed shot SD. And it could be argued that it's supposed to look a little cheap and crummy, so a Blu-Ray upgrade might well defeat the purpose!
I'm afraid I'm 100% to blame for the original's absence on Blu-Ray. When I made the deal for Sony to acquire the film, I stupidly made it a perpetuity deal, thinking I would be at the studio a lot longer than I was. Since then, the rights went to Mill Creek as part of an enormous package deal...