Plenty of other top-tier tennis players build muscular strength, Roger Federer, Andy Rod****, Andy Murray, and the Williams Brothers.
Obviously they're not trying to get to pro-Body Builder size, but the do build muscle. Build it right and you'll be both explosive and strong. They're not doing isolation exercises (isolating a single muscle, e.g. dumbbell curls for biceps) but compound exercises which strengthen several muscles at the same time, such as squats and leg presses. They also incorporate a lot of bodyweight or light-weight training (e.g. medicine ball) along with good stretching routines.
I found an article with what appears to be some good advice, give it a read.
