Prior to the ruling, the company was already mulling to make some changes on its own, including targeted throttling and a 250GB cap on bandwidth per customer. The reasoning behind the appeal, then, is not to go back to their dubious practices of discriminating against specific types of data (read BitTorrent) but rather because Comcast – and the rest of the ISPs and telcos – don't want the FCC to be able to tell them how to manage their networks.
Comcast argues that the FCC’s sanctions against it were based on a list of network neutrality principles, not laws – thus it had not broken any law. Whichever way the court’s decision swings it will set a very important precedent. If the FCC’s order is recognized as unlawful by courts then other ISP may follow in enforcing network policy as they see fit. On the other hand, if it stands, it would grant the government fairly broad authority to regulate the Internet – and possibly lead to ISPs increasing prices for perceived bandwidth hogs.