The department cannot test all possible alternate configurations of PCs to determine suitability. Some of the software used in classes has a complex user interface, and thus it is hard to use if the monitor is too small or the resolution supported by your graphic card is too low.
Computers get less reliable as they age.
By Murphy's law, computers tend to break the night before a computer assignment is due. Ideally, you should have multiple years of an on-site or overnight replacement warranty program covering your computer to allow rapid repair. In later years, you may feel that you're at a disadvantage because classmates can recompile and debug code faster on newer machines. You may wind up having to replace the computer in a later year of school, or worse, feel that you have to do it in the middle of a semester. Be prepared for the expense as well as the time for moving software from an old to a new machine at that point in your study.