Positions of instrumenst in stereo

Curious question for all you music recording folk. I was listening to my iPod the other day and I was doing some real critical listening. It made me think Is there a rule or industry standard for placement of instruments in a recording? It appears to me that there is none. One recording had the piano in one channel and a lead guitar in another the drums were centered while the next track was totally different. All of the music I listen to is what I call "Classic Top 40" from the 70s to 80s. I thought I read or saw somewhere that there was "agreed" upon recording techniques. Am I missing something? Also what makes someone want to put certain instruments in certain channels. Is it the recording engineer's, the producer's, the director's, the artists' idea or all of the above. And would the recording have been a #1 hit had the lead guitar been in the right channel rather than the left?

there was/is nothing that resembles any type of standard

Different A&R people, different producers had differing approaches that ranged from twinkling concept to theories.  It was status of individuals not the ideas that controlled how influential the approaches were

Bass frequencies are going to be inherently less directional and the scale is probably logarithmic, or at least not linear . . . which simply means that listening in ambient space (non-headphones) lower frequencies will be more difficult to position discretely.  But increasing dependence on artificial reverb (during time you listed) means that spatial relations will be smeared anyway and tend to be controlled, at least partially, by techniques other then pan & dolly

over the years I think I've not merely been exposed to but have used several thousand approaches to suggesting 'space' in a recording.  Anymore it becomes one of the arrangement variables.

Bass frequencies are going to be inherently less directional and the scale is probably logarithmic, or at least not linear . . . which simply means that listening in ambient space (non-headphones) lower frequencies will be more difficult to position discretely.

The transition area isn't really logarithmic - its just the area where there is trading between IID and ITD, depending on the amplitude and timing of signals, and the band in which ITD operates extends up to about 750Hz. But the interrelationships are complex, so the trading band actually extends a little higher than this at some angles. There's nothing 'inherently' directional about bass - okay, it's much easier for it to ignore small objects and roll straight through them - it's the manner in which our ears work that seems to make it less directional.

It made me think Is there a rule or industry standard for placement of instruments in a recording?

As oretez says, not really. In recent years it's become rather more normal for the bass part of thythm sections, and vocalists to be panned dead centre, with the rest of the rhythm section panned around them symmetrically from this point (simply because this makes for generally acceptable mono, when it's required), but as far as everything else is concerned, all bets are off. I have some relatively early released recordings where the vocal is the only thing on the right channel, and everything else is on the left. This sounds truly weird in stereo, but does represent the other 'acceptable'(?) way to achieve mono compatibility.