This bird is currently using a Windows laptop that is 4+ years old. Will the Mac last longer?
Hard to say, at this point. When I was using a Windows-based laptop, it felt somewhat archaic right away and - while it still runs - can barely be used for modern tasks. My Macbook Pro is now 3-4 years old and still feels fresh, even for some more demanding tasks.
While it's tempting to chalk the difference up to Windows/PC vs. Mac, it could just be that the rate of advancement is slowing (if not in terms of hardware power, then in terms of being able to and/or needing to utilize it). Macbook Pros still have a better build quality, overall, which is reassuring in thinking that they'll last forever...
It's also worth noting that batteries are integrated these days. I've twice had to swap out the battery on a Macbook Pro before, right around the two year marks on each of them (Apple actually replaced them for free). On my current Macbook Pro I'm getting the "service battery" message, too. Apple changes the battery for you on the systems where it's built-in, so it's not like you need to trash the entire system... and the newer batteries supposedly last 3-4 times longer than the type that I'm using. However, it's the part that's most likely to fail and need replacing, and it's not user-serviceable anymore.
It's worth at least checking out the MacBook Air. For long flights, its reduced weight will be well appreciated.
I'd only suggest a Macbook Air to people who really need (and I mean
really need) the portability. You're exchanging power for a thinner form factor and lighter weight. I've also heard of overheating issues with the Airs for people who try to use it for heavy tasks. Maybe the newer ones have fixed those problems, but... choose the right tool for the right job.
It's not like Macbook Pros are that heavy, either! Why, I remember when desktop replacement systems used to weigh closer to 10 pounds - Macbook Pros are nearly half that! And so thin by comparison! Sigh, I'm becoming an old person...