[Eric]

In the lesson Capo Lane, it says to play a G/B. Now, from what I have learned from this website, that means to play a G chord with a B bass--right? So, to me that means place my fingers in the "G" position with fingers on the 6th string 3rd fret, 5th string 2nd fret and 1st string 3rd fret, but don't play the 6th string at all--but rather let the first note be the B on the 5th string (2nd fret) for the bass note. I'm ok with that--that is how the 2nd measure of CL goes. It allows me to play where my fingers are position--the B bass note and then the G on the 1st string. However, the chord "suggestion" on the third measure shows a G/D which (using the same logic) would tell me to not play the 6th or 5th string, but to position my fingers for the G chord once again but this time start the G chord on the open 4th string which would be the D bass--and then play the remaining 3, 2, and 1 strings if needed as part of the G chord. But the next note in that measure is a C on the 2nd string which is not part of a G chord. So, why am I asked to position my fingers as a G chord? Why not a chord position in which at least one of my fingers will be sitting on either the C or D on the 2nd string which are the next 2 notes? This way at least one of my fingers are already in place.

[Fretsource]

Because that C is a non-chord tone. The real music that you play is in the tab. The chord symbols are helpful in telling you the chord name and showing you its best shape for the notes you're playing - but they're constantly modified (in the tab) to include the non chord tones.
A lot of tab readers don't even bother to look at those chord symbols. The tab tells them everything they need to know.

[solidwalnut]

I guess it really depends on the tune. But I have to wonder if this particular song is giving the idea that the bass guitar is actually droning on those specified bass notes, but the guitar is actually playing something else closer to the regular chord...Sometimes chord annotations are like that.

Steve