150 mph covering 100 ft with a bounce... I'll take that over facing someone slapping a 6 oz vulcanized rubber at 90+ mph standing 10 feet away. No lie, my team mate lost one of his testicle in a game.
Offensively again, try deflecting the puck in the air with a stick blade only 3 inches wide from a 90 mph shot inside 40ft.
Unless you are standing 20 feet behind the baseline, you won't be 100 feet away from the 150 mph serve.
Regardless, every sport at different levels pose different sets of physical and mental needs. Tennis at the recreational level, with balls being pushed, dinked, and bunted back and forth, is not much more difficult than backyard badminton.
Yet, badminton and tennis, both played at competitive or tournament levels require training, proper learning, ample athleticisim, mental toughness, and more. (Try returning a shuttlecock traveling at 150 mph standing only 30 feet away!)
Watching Nadal and Federer play this morning on television, most players can't imagine what a 20+ ball rally involves in terms of footwork, racquet control, spin, and endurance. Not to mention, they often follow up these rallies with similar rallys after only 20 seconds of rest.
From a professional stant point I appreciate this aspect more than just the stroke components. As a 5.5 player, if I get into a 20 ball rally--even at speeds that are not on par with Fed and Nadal, I'm really winded...and I am in good shape. (Ok, I'm 48 years old...but, still!)
Show me a football, baseball, basketball player or boxer, hockey player, or any other sport player who could stay out there doing that kind of sprinting, hitting, touch, and power, for three consecutive hours (without having a 20 minute 'intermission' or opportunities to sit on the bench for a good portion of time!).
I'm not saying that other sports don't have great or even greater athletes. I have always admired basketball players being able to pass, dribble, shoot and go up and down the court for relatively long periods of time.
One of the hardest things I have ever done was wrestle in my high school phys ed class for three minutes!
And, I don't think I have ever been as tired as racing canoes at Disneyland for 4 minutes...probably the most exhausted I have ever been!
But, tennis, as mentioned, uses a great many skills, a great amount of mental focus, and tremendous endurance at the highest levels. You won't see too many top ranked men or women players have a big gut, flabby or simply out of shape!