Most of the recordings (notable exception--the James Gang clip) had studio-enhanced additional guitar tracks. The combination of Guitar-bass-drums, no matter HOW brilliant the guitarist, can sound a little empty live. I know, because I played in such a group for a while. We did have a rhythm guitarist, but we still did gigs as a trio when he couldn't make it. We did fill in more on many numbers, because besides playing the bass guitar, I also played keyboards using my right hand for the organ and the left hand doing a keyboard bass, like the Doors. The Doors were essentially a four instrument trio, with Ray Manzarek doing both organ and bass. It wasn't as hard as I thought it would be. Of course, having Morrison as vocalist and front man, especially when he was sober, helped a lot, too.
If you listen to "Crossroads" on the live part of Cream's "Wheels of Fire" double album, you'll hear that even with Clapton's virtuoso solos, the sound is a little sparse with just Jack Bruce's bass to fill in. The lack of a middle range instrument, whether a rhythm guitar or a keyboard, is really noticeable. Even Hendrix, who was brilliant live, had a second guitar track behind his lead on the Crosstown Traffic recording, as did Cream on the clip in this thread.