Both are 12 bar minor blues. Now folks minor blues is a totally different animal than typical blues with dominant 7 chords. It is no longer derived from the harmonized major scale, but derived from melodic minor or harmonic minor, that kind of thing. As I study Jimmy Page stuff combined when Robert Plant could hit the really high notes (early 70's), I feel they were making a statement with each genre based song. Can you top this? And nobody could. The Thrill is Gone is a classic of course, maybe even boring. But Since I Have Been Loving You sounds like an epic, orchestral masterpiece, but there are only a few chord differences in the embellishments and substitutions in the turnaround area of the 12 measures and the key is up a step.