ASA is the american linear standard and DIN the internation logarithmic standard. The ISO value is a combination of both. So (at least with analog film) you have two values. The ASA + DIN (in degrees).
With digital cameras ASA = ISO.
There is a way to shoot with multiples of ISO 160 even with a T2i, if you use the Magic Lantern firmware.
From experience I can definitly say it makes a huge difference concerning noise.
That's the cool thing about Magic Lantern. It's installed on the card, not the camera. So, if you switch on your cam with a card that has Magic Lantern installed, Magic Lantern boots (takes about 2 seconds). If you use another card or format your card: Magic Lantern is gone.
I don't want to miss ML for my T2i. Really a cool piece of software!
What I personally like best (next to the ISO thing) is the built-in follw-focus, the focus-peaking, the possibility to see the histogram while recording and the q-scale function that allows to record in higher (or lower) bitrates.