I had symmetric 10Gb for over a year, until they sent a new modem. When I tested the speed again, it was asymmetric. I figure it's the new modem, but the change may have been made before. I don't usually upload >1Gb, so I didn't notice when it actually happened.
I'd ask support, if you care. I just took a glance at the forums over on forums.sonic.net, and I'd expect a huge outcry about such a change, and don't see anything. Agreed it doesn't matter in principle (hell, I can't ever use more than about 1.25Gbps even on download), but the downgrade would bother me.
