Prog rock is totally universal, anyone in any country and using many different styles can play it, there's been prog rock bands from every continent covering a wide variety of tastes around for 50 years. Southern rock is - by definition - one basic style of music, and concentrated mostly into maybe 9 of 10 states inside just one country, so whilst I like some of it (especially Skynyrd and Little Feat, two of my all time favourite bands) for me there's no comparison.