Why do iPhone's seem to last longer than Android?

When they're brand new, Android seem to be quicker than iPhone's but over time they seem to slow down and become sluggish at a much faster rate than iPhone's.

I have a Nexus 5 and I love it but I can't help feeling it won't be much longer than a year before it slows down. My dad has the Nexus 4 that he only bought around 11 months ago but it's quite often not as quick as it was - apps take longer to open and even if an app is already running in the background, it'll take longer than it should to open. It's not annoying, just concerning.

Whereas an iPhone 5 (also a year old) seems to fly by like new. A few of my mates have an iPhone 5 that they bought a year ago and almost no sluggishness is evident.

My N5 is amazing but why do Android phones seem to slow down more so than iPhone after a year or so? And is this ALWAYS the case or does it depend on how you look after it?

It depends on how much useless data it has accumulated. As a variety of Linux, Android tends not to forget and eventually it gets constipated. It's worth saving all your important data and returning the phone to factory conditions every now and then - a bit like a PC really.

An Android is like a PC, which means that it is also vulnerable to viruses. Whereas iPhones are not as vulnerable. One point that Apple uses to help sell their products is that you won't have to worry about viruses anymore. If any viruses for their products pop up, they put a stop to it. That's one of the reasons that every couple of months, an update comes out for their products. I'm not saying that its impossible for Apple's products to get a virus, but it is much harder. Also, their products do tend to slow down as the years progress, it just doesn't occur as fast.

Android phones have quicker processors than iPhones - fact. If your Android slows noticeably then there's maybe a problem or too much accumulated junk on it. IPhones are also far less reliable than Android phones and as a previous answerer stated, they are only open to Apple's own apps whereas Androids can access apps from anywhere.