Mill/Drill Question

[Michael J. Spangler]

alright here it goes. there's been some talk about the Milling machines in HF new sale catalog. i was wondering what the classifications meant. i've seen them labeled differently before.
Geared Head Milling/Drilling Machine
Vertical Milling Machine
Heavy Duty Milling Machine.
what do these named add up to? versatility? more power? thanks ahead guys