the newest laptop won't necessarily be the most durable or longest lasting.
yes, if you delay buying an equivalent laptop by a year it might finally die a year later than one bought a year earlier, but a MBP update isn't going to mean it suddenly becomes less likely to die within 4 years or purchase (or however long these things soldier on for).
if anything, it seems the newer products seem to have a shorter life. I've been through 3 televisions in 5 years - my parents only recently ditched a TV the same age as me (that'd be almost 30 years old!)