Nevertheless, due to lack of widespread broadband adoption at the time, the Dreamcast shipped with only a dial-up modem while a later-released broadband adapter was neither widely supported nor widely available.
Downloadable content was available, though limited in size due to the narrowband connection and the size limitations of a memory card.
Update: It sounds like new Achievements can be added on the fly - the whole system is less rigid.
From Xbox.com: "Xbox One's all new achievements system has richer detail and spans across your games and experiences, which means achievements are no longer confined to a single game.
There are other, more minor tweaks to your console's activity feed, the speed which you can join friend/follower Twitch broadcasts and improvements to your suggested friends, too.