It's definitely a gamble to not buy it, but saying that not THAT many Macs go wrong. It might look like they do on forums like this, but that's just because people only post when there's a problem (when was the last time you saw a thread titled "Hey guys, my 3 year old Mac still works!") The failure rate is a fraction.
It also depends what Mac you buy. If it has plenty of user serviceable parts like HD, RAM etc, then it's less important. However on something like a new rMBP, it's absolutely essential.
FYI I've had 5 Macs since the late 90s, and 2 of them have required Apple Care treatment within 3 years (HD in my G4 iMac, and screen on my current iMac.) No logic board failures though.