Here are my thoughts on why aluminium tent poles break, just in case it helps some readers now or in the future. The original poster and contributors above probably already know most of this. Also, please note I'm speaking generally here, not about any particular brand of tent or pole.
If a pole breaks on a fairly new tent, with no obvious reason why, then it might be a bad pole section, bad batch of poles, or maybe a poor tent design. In this case I'd contact the brand responsible for repair / replacement poles / new tent / refund. However, I don't think this is common.
If a pole breaks for an obvious reason (e.g. you stepped on the pole / fell on the tent / huge gust of wind with no guy ropes in place), then its probably just the sections that have broken (or bent badly) that need replacing. Anything that looks undamaged is probably undamaged. Get it repaired or replace the broken section yourself if possible.
If one or more pole sections break on an old tent without obvious cause, it is probably fatigue cracks that have built up over time. This issue will affect many of the highly stressed sections in the pole. In this case replacing one or two sections probably won't help much, as there are other sections that will also break soon. Replacing the entire pole set is the best solution. Of course, this only makes sense if the fly fabric, zips and floor are still OK - if they are wearing out too, I'd suggest a new tent. Poles tend to make up 30% to 40% of the cost of a tent.
Fatigue cracks occur where there is a fluctuating tensile stress - and usually start at some point of damage which makes the stress higher at that point. Once a crack starts, it tends to grow a microscopic amount every time the stress changes, until the structure is so weakened by the crack it fails suddenly and catastrophically. There are two main implications for tents:
If the poles are damaged, they can start to crack sooner. The main point of damage is the open end of a pole section, where the ferrule of the next section slots in. If you flick the poles like a whiplash to assemble them, you tend to create small dents and chips on the end of the section - and this where the cracking often begins, as the open end of the tubing is very highly stressed in use. Sometimes you can see the cracks on old poles. So: assemble the poles gently and try not to flick them about.
If the poles move around a lot in the wind, any cracks present will be growing faster. When the poles aren't moving around (i.e. slightly bending and unbending), the cracks are not growing longer. So: use guy cords and other means to keep the tent poles as still as possible. If the tent is flailing about in the wind, the life span of the poles is gradually being used up, even if they don't break on that trip.
I'm interested to hear if anybody has any other opinions or experiences.
Finally; nothing lasts for ever: tents are made to be used and enjoyed. In some ways, wearing out a tent is a sign you've done a lot of trips and had a lot of fun - something to be proud of.