Just going to throw my two cents in here to defend truck pushing.
First of all I've started to try Starcraft 2 recently and I've learned that there's a thing called cheese. This is where one player goes for attempt to end the game quickly by attacking their opponent first. This is usually an all in tactic as if it fails you will be considerably behind.
Truck pushing is a form of this cheese yes but that being said it is still something that should be allowed within the game and shouldn't be considered a game breaking mechanic. The truck is incredibly slow already and only acts as a scouting unit in the first few minutes of a game. Players that take the risk to use this unit in combat to win engagements should be rewarded if they pull it off correctly. Let me remind you that if the truck is destroyed this set's back the OKW player considerably for obvious reasons.
The truck push can be effectively countered by just simply not engaging in the first place. Secondly as both allied factions can field a light vehicle in order to quickly counter this unit. Those being the M3 and WC. Furthermore both factions can have at grenades at the start of the game with the upgrade from the soviet HQ and vetted rifle from the rifle company.
I shouldn't be forced to go a certain doctrine as US forces just to counter a stupid truck