The hardware specs are "meh" at best, but the build quality is still better than the competitor..
I have a newer Thinkpad for work, and it feels cheap and plastic compared to my MBP. The Lenovo creaks when I pick it up with one hand, and just feels flimsy. The MBP feels solid and integrated.
It's their thin-is-better lighter-is-more-important model.
In the traditional 14-16" size, the T4xx/T5xx devices do what they are supposed to. A changable battery (while running, without tools) enables you to do things like swapping an empty battery for a full one, either by plugging in shortly, using a secondary battery in the case, or briefly shutting down.
I don't want to carry that much energy with me all the time, but I still want the option to use the device without having significant downtime. A short break is fine, but that's 5-10 minutes, not 30+ for charging the battery.
They have a price point where they can be made solid and well put together. Lenovo also sells cheap laptops of lower quality. Not sure why that's a problem. Or do you think people shouldn't be given cheaper options?
The Air is an exception—it was in this limbo where it looked like it didn’t have a place in the product lineup between the MacBook and MacBooks Pro. A couple of exceptions is hardly “usually.” The other lines are updated regularly with whatever is the latest in October.