Thanks for good answers!
Anybody know why ATI made the cards that way? what is the reason that we cant use 6x dvi? is it to make displayport more known?
ATI said it was about keeping the cost down. Using displayport to drive the 3rd + screens made the cards only a little more expensive which was important at the time because they didn't really know how popular eyefinity would really be or how soon and how good or cheap the Nvidia cards would be.
As it turns out they had no competition from Nvidia for a long time and eyefinity was quite popular but they didn't know that at the time they designed the cards.
why can we have as many vga as we want but not dp til dvi?
The VGA adapters actually convert the Digital displayport signals into anologue VGA and manage to aquire enough power from the displayport to accomplish this up to around 1080p resolution. So these adapters are Active.
The cheaper DVI adapters do not convert the signal. They just pass through one of the available DVI signals over the displayport so they are passive. The active DVI adapters require additional USB power and are a lot more expensive. I am sure it would be possible for someone to make a lower resolution DVI active adapter that is powered from the displayport but there was no market previously for such a device and they are making a lot of money on the dual link devices.