Anti Viruses...

I was in a computer store sometime ago with a frnd of mine to get a solution for software incompatibility in Vista when i noticed a rather tensed lady being attended on a nearby table. Her laptop had been infected by some virus and the person attending to it was offering a rather expensive solution for it.
The 'engineer' told her that he would first make a backup of her hard disk(Rs.250), then format the hard disk (Rs 400 if the sys was in warranty nd Rs.500 if out of warranty), then restore the contents and she would have to buy a new LICENSED ANTI VIRUS for protection(cost depending upon choice)
Now what i could not really get was that if the anti virus was that much afective in curing then why the hell was there a need to fomat the hard disk?
And moreover the lady already had an updated anti virus in her system at the time of infection!

So what was the guarantee that the new one would keep the sys safe throughout its licensing time?
U know what struck my mind was that who in the world was having so much of spare time to take pains to create complex algorithms to infect a system of which he probably would never know.
And why the hell are all these viruses so easy to detect by these anti viruses....i mean all programs work on set principles..so an anti virus would be looking for certain specific tasks and so why does someone need to write a message on ur desktop to make u aware of virus infection...viruses r meant for targets and why would a programmer add a loophole to get it detected?There r patches available for nearly everything so how in the world can a virus programmer be so ignorant to let his algo be destroyed by some stupid anti virus???

Hey even a bigger question that struck my mind was that how could there be possibly cure for so many threats being constantly casted upon?I mean 1 minute u hear of a dangerous virus and the next minute a company comes out with its cure...as if it was all pre meditated...as if the threat was already known...as if there was some sort of understanding between the virus and the anti virus...u go threaten to infect and i will come to save the day!!!
And most of all the real viruses still go undetected...they do their work and vanish and most of the times u would never know u had an infection till the disease is fully grow..UNCURABLE....