Apple made plenty of purchases, but they were always small. The two largest were Next in 1997, which brought Jobs back to the company, and PA Semi in 2008, which eventually lead to the Ax ARM processor line in the iPhone and iPad.
The Beats purchase was Cook thinking big. Some joked that it was appropriate that Apple would pay too much for mediocre hardware, but Cook wasn't after the headphones, he wanted the streaming music service Beats was building.
That too seems an odd decision, because Beats Music has had a very slow start. Hopefully this is not the start of Cook making some bad, Steve Ballmer-like massively overpriced acquisitions.