> You would not bother to build a whole infrastructure just so that you can buy a bow or a shield.

We're talking about a forge here. That's hardly a crippling investment :P

> Okay: One hammer, one flag, one tentpack and 7 blocks of stone would allow you to quickly build up a base behind enemy lines with the ability to buy stuff there ;)

What's the point then to have a tent, when you would always construct it right next to your flag? If you have a tentpack, it even works mostly the same as flags.

Sorry, so far you don't have me convinced in the slightest. Here's another one of my spontaneous list of arguments for buying-at-building:
* We have a building less
* We don't have to build all menus two times (for building & buying). And the buying one won't be as big.
* We have reason to show off all our nice production buildings even in fast-paced melees
* Potential of strategic gameplay, like killing the enemy forge
* Natural delay for buying a lot of stuff (needs to be produced)
* No tent bombs

And last but not least:
* Generalizes naturally to buying buildings :)

Your idea strikes me as more conservative, which is okay, but I would really like to try this.