Over the years it becomes brittle enough to break off, typically at the cement floor of the basement.Homes that used the pipe from wells do not have the problem as there is no chlorine.

Some knob and tube wiring is still rubbery and well insulated and still very usable, but some is brittle and the insulation cracks exposing energized conductor.

You mix the shrink/swell cycles of the underlying soil and get some differential settlement across the slab and foundation cracks happen.Stucco, like brick, is a very brittle material that is unforgiving to foundation movement and cracks easily.

Insulators crack, insulator nails work lose,wires get chewed by critters and fray, connections are brittle, terminals almost welded shut, fuses can be hard to find that are properly sized for the electrical run and boxes and runs are usually ungrounded.

In my area there are some old house with clay sewer pipe which are brittle and more prone to break or fail because of root infiltration at the joints.

Nothing high dollar but nothing cheap and brittle.

The inspector found that the Roof, that looked great from the ground, was extremely brittle. 

It is usually very brittle, but the siding on my rental is actually kind of soft and is more of an asbestoes-asphalt emulstion type material that I was not familiar with and it took me a while ot figure out it was asbestos.

We re-plumb water lines with PEX for 2 reasons: 1. lower cost, easier install, 2. no copper theft threat.Many of these properties have brass or galvanized lines, which become clogged and brittle over the years, so you'll need to have an experienced plumber if you are repairing/replacing fixtures in the kitchen or bath. 

Some of the problems are that the wire can become brittle, the insulation wears off over time, the porcelain insulators may be broken, it is ungrounded and all the splices and additions to the circuitry is more of a load than these old systems were ever supposed to carry.