Why ACI 318-08 increase the limit of Agfc? /10 to Agfc? /4.?

[alberick]

In the latest version of ACI 318, the section 21.6.4.6 increased the limit to apply its requirements, but i'm not sure if uses the omega factor of ASCE 7-05 for walls systems of 2.5....but locally may be can generate higher forces and the supporting elements can become very highly overload..

What would you do for column supporting design if considerate that capacity in flexure of supported wall it's reached ?

Thanks.