Here's my quite biased view.

Most martial arts, unless you reach the highest gradings, are not a great deal of use in real life. People can spend years training, but if you're not used to taking a punch, when it happens for the first time, you will be far too dazed and disorientated to do much. I did Muay Thai, for a few years, and spent the first few months getting the crap kicked out of me when sparring, but then later down the line you realise you can be hit and recover from it, while still thinking on you feet. Also Muay Thai is quite violent, using your knees & elbows which in a self defence street scenario would enable you to strike and run! It's probably why a lot of the ultimate fighters and mma's have a grounding in muay thai, as it's quite useful until someone takes you to the ground (then you need wrestling etc) not only that but it's still useful as a beginner.