Motherboard do tend to bend, specially A64 and S478 mobos. This is due to the clip design.
thats why you will see many new motherboards coming out with a metal reinforment plate below the motherboard.
It shouldnt worry much if mobo is working properly. In US you can buy those additional reinforcement plates for mobos which dosent come with one. I dont know the status in India.
It depends on the motherboard, manufacturer, quality of PCB vinyl and also on the HSF.
My old gigabyte AD77pro devloped nice bend with Swiftech HSF. Still working fine with the guy i sold it after 4 years.