You mean the hardware engineers they brought onboard when the bought NeXT (OS X)? How about Lala.com (iCloud)? Fingerworks (iOS)? Soundjam MP (iTunes)? We can just go on and on here [1].
None of this is to say they don't have brilliant hardware engineers working on things all the time. But the boldest moves Apple in the past decade and a half have come from strategic M&As.