I agree, I always take a quick glance over my shoulder and it's saved me a few times over the years.
Having said that I did a little test going down the dual-carriageway and I can clearly see cars in my peripheral vision before they leave the mirror ( even without the blind-spot convex part ).
This was on the driver side mirror, perhaps they are designed so they don't need the blind-spot bit.
I find it surprising they would have removed them without a reason as the old A3 had them.