Things you CANNOT DO without passing milestones:
(a) Get rid of penalties from Raise Dead
(b) Use more than 1 magic item daily ability (per tier)
After a number of milestones, it is possible to go "more" nova than before.
In general though, the 15-minute workday is going to come up less often because:
(a) The encounter system is vastly different than 3e. Back then, the encounter system was supposed to wittle you down over time so that the LAST encounter is a nail biter ... it was about conserving your resources. However, you could always overspend your resources and have a bunch of easier fights and just rest a bit earlier. Eventually, certain groups basically embraced the idea of a the 15-minute workday where they would be one REALLY TOUGH encounter where they have to go nova, that way there is a challenging fight that doesn't rely on the players to "hold back" for it to be challenging.
(b) The DM doesn't have to feel as bad for attacking a group during an extended rest to discourage the 15-minute. The party, even if it's out of daily powers, will still have all their encounter powers available, and if they just went nova then went to bed, they can't possibly be out of surges, as there is unlikely to be enough ways to spend their surges during the course of a single encounter.
So, the benefits of the 15-minute workday are reduced, the penalties for going on even after nova'ing are reduced, you can get back some of the stuff you get back while resting by continuing onward, you have a limited number of ways to use up some of your daily resources, like your healing surges, during a single encounter making it hard to use them all up, the players are still pretty solid after they use up all their daily powers, the DM is able to attack the PCs at night and the PCs will still have most of their powers available.
The 15 minute workday is still an option, but it is no longer a great or obvious option. If a DM doesn't like it, they can force the players to move on by having the encounters "come to them" when they try to sit around for about 18 hours to get their extended rest (about 12 hours to get access to the 6 hours of rest). The PCs aren't getting set up for slaughter ... as they probably would if a similar group were to nova their spells in 3e. In 4e, losing their dailies for later encounters might suck, but hopefully they'd learn that encounters and at-wills are often enough, and in the future using their dailies wisely and plugging along instead of trying to go for the fastest/easiest way isn't going to fly with the DM.
Summing up: In 3e, you pretty much had to TPK to punish the players for their 15 minute workday. If they nova'd the first encounter and were tapped out, and you sent another encounter in, you'd likely kill the party. In 4e that isn't the case. Can you nova in 4e? Yes. However you still have a LOT of fight left after you nova, and thus the DM isn't put into the situation of "let them rest or they WILL DIE" that they were in 3e. So the DM can basically sit the players down and say "You aren't going to get away with one encounter per day, unless it's a special situation. If you want to use up all your dailies in the first encounter, that is up to you ... but that's not a good enough excuse for needing an extended rest."
The 15 minute workday is, in part, a DM/player issue. 3e encouraged it more than 4e did because of the way resources worked, and the way that encounters worked. Encounter powers and healing surges (and ways to trigger healing surges during an encounter) are all helpful in extending the adventuring day.