It depends.
If your hardware starts to degrade, but fail-safes kick in to ensure the hardware still runs, you can have slower hardware. An example is a hard drive that progressively is worsening, regardless of wipes. There are multiple factors that go into that.
But the main two things you can look at are:
- how much Apple decides to slow down the laptop through minor updates, and major updates to OS X
- whether you can replace your battery or not
What you can't bet on is what sort of tech will come out. If in 10 years the only difference is in minor upgrades (faster cpu, faster GPU, etc), then ya... what you have now might last 10 years. But let's say there's major Wi-Fi tech changes, a bunch of other unforeseen tech improvements, new software features that are utilized through new tech, etc... you might really want an upgrade before 10 years is up. A single example might be with the future of force touch trackpads, and how you might interface with the MacBook Pro. Or, let's say in 10 years we see a major storage speed & capacity improvement, alongside major internet bandwidth improvements (let's say the average storage base becomes 10TB instead of 256GB, and internet download/upload speeds increase by 20 fold), then there's another reason why old tech might go out the window.