IP - Have they removed HDMI ports from most laptops now? My cheap netbook had one six years ago but most of the refurbished lenovos don't have them now.
DisplayPort is the VESA standard designed for computer displays to replace older VGA and DVI outputs, and is designed to be backwards and cross compatible to output to VGA, DVI and HDMI via mostly passive (but sometimes needing active) adapters.
HDMI is a proprietary A/V standard for home entertainment equipment connectivity.
Lenovo uses DisplayPort.
Dell uses HDMI.
Lenovo's choice is smart and more flexible, especially in a corporate environment. Dell's choice is just being cheap and pandering to the lowest and most common denominator. (It's a shame the Lenovo Thinkpad T/W/X x30 series are the last Thinkpads I'm comfortable recommending, as the build quality just isn't there anymore - and even the x30s are almost borderline, honestly. Dell's build quality, however, is still there.) Anyway, most people don't give a fig about the true superiority of DisplayPort as an output standard for computers, and just focus on wanting to connect to an HDMI television with their laptops and grouse about needing an adapter to make it work.
In the case of the T430 specifically, it uses Mini DisplayPort on the laptop with the optional docking station utilizing the full size DisplayPort. There are penty of cheap, passive mDP to HDMI dongels that should work with the laptop including one from Lenovo specifically (p/n: 0B47089).