Lenovo and IBM Thinkpads share the same name but are completely different products.
IBM is a logistic company and they made Thinkpads back in the day where notebooks were considered durable business assets. They designed them so they would stand abuse and be repaired and upgraded easily. They knew businessmen are more rational when making choices so they would never complain about an ugly machine as long as it was well designed. So they went and designed it with important considerations in mind such as ergonomics, familiarity, expandability, etc. Thinklight, for example, is much more than a light to see the keyboard; it's probably the only comfortable way to read a printed document in a dark room. The modular bay offered lots of options, just a few that come to my mind are: floppy drives, ZIPs, port modules, batteries, secondary hard drives, etc. They charged premium and people paid for it.
Thing is, at some point people started to realize notebooks aren't durable assents. Usually a customer will replace it well before it fails or becomes obsolete. So notebooks became sort of disposable and as such, people was not so concerned about the premium bits and didn't want to pay premium for them. IBM realized this and sold its division to Lenovo.
Lenovo Thinkpads are no longer business models. They are above average quality consumer grade notebooks with some inherited business grade features. They aim for the large audience and in most notebooks today you'll find a six row keyboard with the delete key on the corner. Lenovo knows that's what people is used to and rather than trying to re-educate the large audience they felt it was more convenient to re-educate the small Thinkpad cult. It's plain numbers and we're far less.
Why are Thinkpads so large this days? Well, one reason for it is that Lenovo wants a touchpad there at all costs. It wasn't a bad idea to add one back in the T4x days as it was a 4:3 design and there was more than enough space for it, but today it's plain stupid. With an ultra-wide screen and a seven row keyboard there is not enough space for a decent sized touchpad unless you make the machine artificially tall. A business user will probably accept the tradeoff between size and the loss of touchpad. After all, it's redundant, Thinkpads up to T30 (and even X200) sold well without it.
To make long history short, IBM did what they considered more adecuate and business users just trusted them on that. Lenovo just does what they believe market demands even if it's flat stupid. Hey, and how could they not? A Thinkpad sells today for way less than $1,000.
Main: i5 3550, 16GB, Z68 Pro3 M, 64GB SLC, 320GB HD, GTX 650Ti, 21.5 FHD LED
T420: i5-2520m, 8GB, SSD: 64GB SLC (boot) | 128GB MLC (storage), HD3000, HD (1366x768), 6 Cell, BT, WebCam
X220: i5-2520m, 4GB, SSD: 64GB SLC (boot) | 128GB MLC (storage), HD3000, HD (1366x768), 6 Cell, BT, WebCam, FP