Navin the rate is less because it’s a grey market product and only comes with 30day seller replacement warranty; oppose to the two year canon India warranty. Frankly you will get a better rate at a shop at lamington road, which deals in grey market products or better yet, ask a friend or relative coming from US to pick it up for you.
Better option would be to buy it through JJMehta, they have it with bill and 2 year canon India warranty + 2 GB SD card + a pair of Uniross 2100mah battery and charger (charger is a tad too slow) for around Rs. 10,700.
http://www.jjmehta.com/pricelist/can...al_pricing.htm
If you do decide to buy the camera from them, check if they have it in their
ebay store, they usually sell at a slight discount there.
With regards to the A590IS, it’s a good camera and has same level of manual controls as the A720IS and S5IS.
The only major difference between A590IS and A720IS is in the zoom and the fact that A590IS can only shoot videos at 20fps at 640x480res, while the A720IS can do it at 30fps.
With Canon S5IS, you will get even greater zoom and ability to zoom while shooting videos, but apart from that, it is pretty much the same. In fact the S5IS is in some aspects considered slower than the A720IS and A590IS.
Oh yes IS = image stabilization