I think there were two kinds of bookings in gulberg. One who got from star marketing, and one who were employees of ib and got direct allotment from ib. Since the ib employess were allotted these plots at a much lower price, they are probably willing to sell at a discount to the current rate of star (which is 1.7 million for 30*60). But another reason could be that these ib allotted files are
Only files without balloting, where you do not know the location, it could be in some far off block.
Location wise i think gulberg is one of the better locations in zone v, since the main entrance is just 1.5km from koral/ airport chowk (which in itself is 10 km from zero point), and normally the traffic is reasonably flowing uptill koral chowk (from zero point), since it is almost 4 lanes in that direction, if you include the heavy traffic lane. I think on the gulberg expressway (200 foot wide), the 6 km distance from the isb expressway to gulberg residencia shouldn't take more than 7-8 mins.
I am not sure about short term (1 year) outlook, but certainly in medium term (2-3 years) time, when they have the bridges and roads in place (also if they can connect to tramri chowk / park road which will allow it an alternative route to downtown isb, bypassing the highway, i see it as a much better option to other zone v societies.
As the population increases further in zone v, the 6-8 km extra on the narrow road after koral check can easily take an extra 20 mins. So location wise gulberg will be more preferable.
Also their farm house location is very appealing, right at the entrance to the isb expressway. Overall i think it has many things going for it. That is the reason more than 5000 people have booked plots there. But as with everything in pakistan there are always risks weather the society will be able to develop and maintain that development. I have a feeling that since it is the ib of pakistan, they will be able to come up with the funds some how. Another thing is that most of the roads etc are already there for some of the earlier blocks. And you can clearly see the work on the ground.