Muay Thai v Kickboxing and other MMA related questions

It seems that many UFC fighters have training in, or even specialise in Muay Thai. Like BJJ and wrestling it seems as if Muay Thai is one of the essential ingredients to modern professional MMA. But what is the difference between Muay Thai kickboxing and American/regular Kickboxing? Does it have something to do with the rules on clinching? Why has Muay Thai become more predominant in the arsenal of fighters than regular Kickboxing? Secondly GSP trains with Freddy Roach who is a world class boxing coach. If kickboxing, whether regular or Muay Thai involves punches why does GSP train specifically in boxing? I heard Freddy say that when he trains MMA fighters he has to remember their stance is going to be different so can't even train them in the traditional ways of boxing because of the takedowns in MMA! So is GSP actually adding anything to his training regime by incorporating boxing? I saw his fight against Koscheck and he used his boxing to dominate and outwork Koscheck, so I guess there is justification for it but again what's the main difference between using a boxing jab to a jab or punch learnt in kickboxing? It's these little finer points about MMA that I'm really intrigued by.

The differences with Muay Thai & the K1 style of kickboxing is that no elbows are allowed, clinching is only allowed for 3 seconds I think, you cant grab around the neck & knee to the face consistently, no grabbing your opponents leg when he kicks & sweep the other leg out, although this happens its not scored, Muay Thai fights are often over 5 rounds rather than 3.

With regards to what you have called American/regular kickboxing is basically a modern contact karate where the opponents where shin & foot guards/pads, they generally kick with the feet & is mostly semi contact & scored appropriately & generally you cant kick below the waist or upper thigh. For me its an outdated form of kick boxing, the japanese, Chinese & Thai styles are better & more useful in MMA & K1, although like boxing you have to adapt them due to takedowns & differences of opponents stances etc.

Interesting points with regards to GSP training with Roach. My take on it is he's using one of the worlds top boxing trainers to get the very best out of his boxing training & although you have to adapt due to the reasons you've given once inside the boxing techniques maybe better & also Roach may have seen something with GSP that he can work with, adapt it & maximise GSP's boxing within MMA. Also with MMA on the rise maybe Roach, who is obviously a fan, may well want to get involved to see what he can offer.

Punches in Boxing & Kick boxing are basically the same but like MMA the kick boxing stance is longer/wider & you have to defend against/avoid kicks. With MMA always evolving I think we are going to constantly be seeing changes in training techniques as different styles with go through dominating times & then get worked out to beat, think when the Gracies style of JJ seemed to be the dominating style & more recently people with a good wrestling background have had a lot of success.

good point about MMA evolving, although I think it can only evolve to a point. There will always be elements of kick boxing, wrestling and BJJ even if fighters might find nuances from other disciplines or refine the techniques.