Yes this helps with positioning and orbital decay. Almost every satellite has this, it isn’t special to Starlink stuff. I know Elon makes it sound like they’ve invented the wheel here, but much of what they do has been done in one way or another.
There are a couple of factors which impact the lifespan of these satellites:
Technological progression. As they refine the technology and techniques they need to update the satellites with the latest and greatest. This means of course removing the old satellite and replacing it with a new one. Especially in the early days (now) this is a huge factor in replacing their stuff.
Failure rates. This is mostly due to radiation, but may also be due to other factors. The network is only as good as its nodes, so failing nodes need to be replaced fast. Radiation hardening is expensive and usually adds weight. This is a trade off between launch costs, the number of satellites they can fit in a Falcon 9 and lifespan of the stuff. Things like solar storms can have a huge impact, as Starlink found out the hard way.
Fuel consumption. Exact positioning is important for Starlink and with their VLEO orbits drag is a big factor. The satellite have very cool engines that help them stay in place, but only a limited fuel supply. There is a safe minimum fuel as regulation requires them to de-orbit safely, which takes a lot of fuel. So just running it till it’s empty is a no go, they need a good safety margin. They also don’t want to start any kind of Kessler syndrome kind of deal, so old spots need to be cleared out before new stuff can go in.
There are other factors, but these are the big ones. Starlink say they are aiming for a total replacement every 5 years, but in practice it’s more like 3 years. This is mainly due to the first batches being more prototype like, getting nearer to a final design recently.
With the proposed 11.000 unit constellation and the 5 year replacement rate, they would need more than 1 Falcon 9 launch each week. The costs are literally astronomical and the revenue has been only a fraction of what Elon sold the investors. I would be surprised if the plug is pulled on the whole Starlink thing.
People seem to think Starlink is the first and only one to try this, but it has been tried for decades and almost all have failed. The only success is with companies targeting niches, where there is little to no competition and premium rates can be had. For example reporters in the field broadcasting from a van to a satellite to be live on TV was a big niche. So far Starlink hasn’t delivered on a lot of the promises made by Elon and is destined to fail unless something big changes.