Same with the Lenovo T-series. You can upgrade both batteries, both RAM chips, the LTE (or additionally a second SSD here), hard disk, wifi, until a cople a years ago the CPU, the monitor, keyboard, touchpad etc. All parts are available from Lenovo.
Lenovo x230 checking in here. I've upgraded/replaced: battery, RAM, display panel, wifi, ssd (both in mSATA and SATA slots), keyboard (x220 keyboards FTW), BIOS (coreboot). The only thing I haven't replaced is the motherboard/CPU, because it doesn't seem worth the effort, even though it's technically possible.
I guess the business Dells are the same?