No, 4 is technically correct. You can get a horizontal position with 3 satellites, but need 4 to get vertical accuracy and you can get positions to the centimetre with 4 satellites. It's just rare these days to have so few. I wouldn't want to...
You could save your $$$ and try Hugin - free, and more capable than all of the paid ones, just a bit more effort to learn to use initially and rather ancient GUI. Don't have much XP with the others, but just checking you hadn't missed the most...
I am looking at purchasing a good Panorama software tool. I looked into PTGUI. Has anyone done the comparison? (side-by-side)? Cost is a factor, but I am interested in the opinion of people who have tried both.