The level 1 wizard in the D&D Next playtest has a constitution of 14, resulting in him having 16 hit points. In 1st edition AD&D a level 1 wizard with a constitution of 14 would have had between 1 and 4 hit points (rolled randomly, although we used house rules that gave him 4 points at level 1). A level 1 wizard in 4th edition D&D would have 24 hit points. Compared to these big differences in hit points, the damage numbers that for example an arrow does aren't all that much different in the different editions. You could kill a 1st edition wizard with 1 arrow, but you need several arrows to kill a 4E wizard. As a result combat in 4th edition D&D takes more rounds than combat in previous editions, and D&D Next is trying to shorten it somewhat again.

Living in a world where pretty much everybody has attention deficit disorder, many people discussing D&D think that combat which is shorter is automatically better. I do believe that it is good for a DM to keep the time for 1 combat round short, which means managing the flow of combat well, being well prepared with monster cards and initiative riders, and not having to look up rules in the middle of combat all the time. I do not believe that a combat having less rounds is better than a combat having more rounds.

My reason for my preference for combat with a certain minimum number of rounds stems from my knowledge of math and statistics. Most people can calculate that if they have a character with a 50% chance to hit a monster and they do 2d6 damage, they will on average deal 3.5 damage per round. What they might not be aware is that for an "average" to have any meaning, you need a sufficiently large sample size. Imagine that character with the 50% hit chance and 2d6 damage facing a monster with 10 hit points. You "average" calculation only tells you that it will take 3 rounds on average to kill that monster. In reality the result is far more volatile: You could kill the monster with one hit in the first round, or you could take 6 rounds or more of low dice rolls.

MMORPGs, who did a lot to speed up combat, usually work with a to hit chance above 90%. But D&D, and that is true for all editions of it, usually uses around 50% to hit chance in the majority of fights. If you plan for fights with only a few rounds of combat, that creates a lot of volatility. In my campaign we had a fight of the 6 player characters killing 10 rats (MMO joke), in which one character rolled only misses for 6 rounds, and another hit only once, in spite of a 50% hit chance. Fortunately we have so many player characters in my campaign, which reduces statistical volatility, but if you run with a group of 4 or less such a streak of bad luck might well wipe your group. Then the DM gets into the uncomfortable position of having to decide whether he should let the group die just because of a streak of bad luck, or whether he should start fudging dice or coming up with a deus ex machina miracle save.

Of course I don't want the group having fights with 20 rounds of combat. I think in 4E some high level monsters have a bit too many hit points, which then got errataed downwards with the D&D Essentials material. But the D&D Next adventure has a lot of fights in which a character can one-shot a typical monster like an orc or hobgoblin. And those are the fights in which a few lucky or unlucky rolls can take the combat all the way from total party kill to being far too easy to be enjoyable. I find combat which is a bit slower but less random, less statistically volatile, is better.