- hardware that can't keep up - an older WRT54GL class device will have trouble routing more than 20-25Mbit/s, which is getting pretty close to what is available from consumer level internet service
- Local speed. Gigabit wired and N-wireless are both valid reasons to upgrade, if you're going from 10/100 and G-wireless.
- Power usage - if you need gigabit networking and have very few devices, it makes sense to not run an older router and a gig switch - consolidating to one device is power efficient and probably pulls less power than older devices.
There are probably plenty of other reasons, but these came to mind immediately.
- hardware failure of the previous device
- hardware that can't keep up - an older WRT54GL class device will have trouble routing more than 20-25Mbit/s, which is getting pretty close to what is available from consumer level internet service
- Local speed. Gigabit wired and N-wireless are both valid reasons to upgrade, if you're going from 10/100 and G-wireless.
- Power usage - if you need gigabit networking and have very few devices, it makes sense to not run an older router and a gig switch - consolidating to one device is power efficient and probably pulls less power than older devices.
There are probably plenty of other reasons, but these came to mind immediately.