I have researched 27 full seasons that I have played, and have come up with only 7 occassions where 30/30 has been acheived. Almost all the seasons were ATG IV
74 Joe Morgan: twice, 30HR/34SB & 32HR/49SB
86 Eric Davis: 5 times, 39/56, 40/42, 35/51, 33/59, & 33/53
My point is that it seems somewhat rare.