Just to provide a counterpoint: I'm still rocking a 3.5 year old Nexus 5 with almost zero evidence of its age (the battery discharges a bit faster than it used to but it's not noticeable enough to even warrant a new battery).
- contacts visible in back cover (the 4 yellow contacts for wireless charging are the easiest to see): https://i.ytimg.com/vi/-RWgjtEwQYQ/maxresdefault.jpg
- spring-loaded contacts in the phone (3 around the camera, 2 on the opposite top corner, 4 match up with the wireless charging points): http://images.anandtech.com/doci/7517/Nexus5-1552.jpg
In mine, the back cover flexes, and contact isn't always maintained for all the connections. I've cleaned them with contact cleaner, and alcohol, tried bending the leaves to provide more pressure, etc. I also replaced the back at one point. Like the original, it would be fine for a while, then need readjustment. The body of the phone has a few thin, brittle parts, which started cracking (the back really wasn't designed to be removed often). I feel like the wear+tear on the phone body and constant mechanical maintenance just wasn't worth it.
Prior to opening the sucker because of the wireless charging not working, there shouldn't've been any finger oils on the contacts (or, I'd hope).
They used to be subsidized by Google and offered at a lower price point, but at flagship levels they have greater competition. I guess it's time for me to consider yet another new territory with this round... device insurance.
You get only 1.5 years it's been on the market for 1.5 years.
Also, Windows at least tells you that support for your version is coming to an end. Google/Android has not notified me in any way that my device is not being supported anymore, that new updates will not be coming, what that might mean for me and what they suggest I should do.
Two colleagues also still use this device, and one is contemplating replacing it because the latest Facebook app won't run on his Android 4.3, and he is not receiving a carrier update. My Note 3 is updated to Android 5.0.
For comparison, my iPhone 5s (that I recently replaced) from 2013, received iOS 10 and was still butter-smooth [1]. It will most likely also get iOS 11 this year.
tl;dr: you should expect/demand more from a device that almost costs a grand.
[1] I replaced it because I wanted more storage and live photos.
I would like to keep using it, but the battery plus the lack of software updates is pushing me back into the market...
(When I become Prime Minister, providing only 3 years of security support for a product that ought to last at least 5 will become illegal...)