Nah, I think it's fine with Macbooks Actually, the MacBook Pro I have is a 2010 model, but it basically has the same processor as a 2008 Macbook. So you could say I bought a brand new computer with 2 year old technology. It really depends to be honest. But the lifespan of a MBP is much much longer than an iPod.
If you get anything with a Core iX series, you'll be able to upgrade operating systems for a long time to come.
Yeah I'm currently on a 2010 core 2 duo, hoping to make an upgrade to a 15 soon to get a quad core processor, starting to feel the squeeze, especially at work!
I suppose a year is worth more on a device with a shorter lifespan