Assuming you buy a good quality and well performing Mac Book Pro, there is no need to renew yearly.
That said, if you are up for an upgrade, having a release 'THAT YEAR' is important. You don't want to force the customer to wait with their old system until it's a year you get around to doing an upgrade. You got an old system, why would you expect to have them buy a system you released a year ago, and will update soon?
And as a company, you might want to get fresh products for new people, or upgrade those who have outdated ones. Buying older tech for modern companies, while still paying full price, seems counter productive and just means more costs in the future as you require or desire to refresh again for the same reasons.
So, we have a few things that matter here. What tech do we need, how much money do we want to spend on that. And how fresh or how soon can we get it?
In my personal opinion as long as there is a yearly release, it is either fresh when you buy it, or soon here, and we wait not too long. That way paying full price for the 'old' stuff, which is from the same year still. Or for the 'new' stuff, because it will be here soon, feels a lot more comfortable.
I am about to buy an iMac or MBP, why would I though? My old iMac is ready for replacement, but they are not cheap, why would I pay for hardware from 2 years ago in last years model. When I could wait a bit and get something new.
But yep, Apple will lose a sale or two here if there's no yearly refresh of MBP or iMac. Because I sure as hell am not buying last years stuff, for that money, or wait until some time in 2017 to get it.
I think we're on the brink of getting new laptops and desktops, and that means it is still 'this year' - hence why I personally don't mind waiting.
But sure is weird that a company that sells us courage for being modern and taking steps to the future, is simply (i guess) doing that, because they know they iterate once, and then not upgrade for years. Yes Mac Pro trashbin, I am looking at you and your underpar performance for 4000 euro, you should have been kept pro. Now you're a black mac mini.
Refresh once a year, whenever it is READY. Don't Samsung Note 7 rush it. And I personally don't mind the wait.
Refresh one year in january, and the second year in december, is not a yearly release. That's 22 months difference. NO cheating!