Yes, exactly, gamerescape already does that. Like I said, there’s no need to waste SE time to add icons for lazy people.
I care about every single gil so I always do research. It is not enough for me to just know that I can buy the item from vendor. I need to know if I can craft it, get it as a drop, get it from leve, etc. If I can craft it I need to know what I materials I need. If I can get it as a drop, I need to know which NPC drops the item. So unless SE can find a way to fit all this info on a tooltip, the icon saying item can be bought from vendor is useless for people who care about what price they are paying.
And if people don’t care about what price they are paying, then why should SE waste time and money?