It's not so true anymore, though. Golf is something that I've enjoyed for a number of years; I was on the team in High School and while I never played a Varsity match I got to play 9 holes 4-5 times a week for 3 months every fall. In the last several years I've been unable to play for a variety of factors: no time, too expensive, no one to play with. I've had cause to pick it up again recently and was at the range for the first time in a while the other day and did some people watching after I finished hitting.
You know what I saw? A shitfuckton of restrictions and movement compensations. A good looking golf swing is a very pretty, violent action. Watch Tiger Woods swing a club and you can really appreciate how intricate it is.
The clusterfuck that I saw wasn't anywhere close to this. What I watched was a bunch of guys who spend 40+ hours bent over a desk with awful thoracic spine, shoulder, hip and ankle mobility try their hardest to recreate what you just watched.
So, what happens to your swing when you have these contraindications?
1) The poor thoracic spine mobility prevents your setup from getting into the best position possible and leaves you hunched over the ball like Quasimodo.
2) The poor scapular/shoulder mobility prevents you from locking your shoulders into a good position and lets your arms swing around like a wet noodle.
3) As you start your backswing, your shitty t-spine mobility won't allow for much rotation, so you quickly transfer the work to your lumbar spine.
4) Your lumbar spine, however, has already been forced into flexion because of your awful hip mobility and lack of pelvic control. Congrats, you now look like the human question mark.
5) This shitty anteriorly-tilted hip position will prevent you from really engaging your glutes and won't allow for any significant power production. This is going to result in some awful weight-transfer that is going to take your swing out of it's groove.