
Originally Posted by
DemolitionSquid
IMO, upgrades should be to make lower tier units more useful as the game progresses into higher tiers with stronger units. Giving tier 3 units upgrades is just silly. For example, the Carrier's increased interceptor attack speed upgrade. If the meta-game shows everyone is getting the Colossus upgrade all the time and never using Colossi without it, it stands to reason they might as well just include the upgrade as an inherent part of the unit and fix its stats to revolve around the saved money.
Of course, that's just how I would design the game. Blizzard obviously prefers a different approach.