Peter Grant really was the pioneer for the way the industry was shaped in general. Peter understood that if the artist was the one creating the music they should be the one making the money not everyone else. Peter was a businessman who knew that control over a career was the most important thing. While most managers sat behind a desk and paid tour managers and other people to be on the road Peter went along with Zeppelin and oversaw everything.
When Zeppelin signed what was at the time the highest advance ($200,000) Peter established production and publishing companies to ensure that the group had control over every aspect of their business, so in essence they never really were tied to the label. The 90 / 10 split was a hefty business deal. After Zeppelin took their 90 percent of the gross the promoter was to pay for all his expenses then take what was left of that 10 percent as the profit. Of course Peter knew that he didn't need to pay a promoter to promote Zeppelin as Zeppelin promoted themselves, so why waste money on a promoter who didn't need to do anything. If Zeppelin did the work they deserved the money.
Radio airplay falls under small performing rights which includes television, radio, movie theatres, etc. and is a nondramatic performance right. Both ASCAP and BMI license this type of performance by granting a blanket license for usage of each of their respected catalogues. The song composition being performed is a public performance, regardless of which artist's recorded version is being played.
Mechanical right is the right given to reproduce the song in a mechanical format (or phonorecords as defined by the copyright law) such as albums, compact discs, cassettes etc. This type of right can be broken down even more to include a compulsory mechanical license which allows another artist to utilize your song without permission as long as the artist complies with the laws set in place to do this.
I admire that you are taking an interest in the profession you may choose to go into. I've seen so many artists so many times get the full steam ahead attitude and relying on other people without learning to protect themselves. So many artists go bankrupt because they just sign the contract without reading it to see the royalty rates and other information and spend money like water without realizing how much money truly comes in after expenses. If an artist relies on somebody else they are likely to get taken. Aerosmith is a prime example of losing revenue to two former businessmen from early in their career. When they signed their contract the two businessmen get their share of the pie whenever certain songs are played from early in the bands career. It's a shame really. Elvis lost millions as well when he signed that piece of paper stating a 50 / 50 split with Tom Parker. That's a hefty management fee.
The days of trust in the industry are long gone. Zeppelin used an honor system of verbal agreements and handshakes by Peter. The amazing thing to note is that Peter never had a signed contract with Zeppelin, and I'll have to check but if I remember correctly Peter received 20 percent for a management fee. He was their manager on trust. Trust went along way in the past but sadly it's gone from the business forever. Good luck in the industry. While this thread really has nothing to do with action figures anymore it's still music related and it's been great to be a part of it.