Several of us watched the Ravens-Giants championship this aft. None of us came up with a decent answer to the question: Why is there a two minute warning near the end of the first half but not the end of the first quarter? Same true with the 2nd half. An explanation of the purpose of the 2 min. warning would be most appreciated as well.
My best guess is that the 2-minute warning is around to provide a “free” timeout to a team that’s trying to drive down the field near the end of a half.
The ends of the 1st and 3rd quarters aren’t really all that significant; teams switch ends of the field, but possession, down & distance, etc. do not change. There is thus no reason for urgency at the ends of quarters 1 & 3 (barring gale-force wind, or some other unusual factor). If you’re driving down the field as the first quarter ends, say, it’s no big deal: you keep the ball at the same field position once the 2nd quarter starts.
The ends of the halves (i.e., quarters 2 and 4) are significant, on the other hand. It’s tough luck for the team with the ball when time expires: who kicks off to begin the 3rd quarter has nothing to to with who had the ball at the end of the 2nd. To simply let the clock run out at the end of the 2nd quarter can represent a wasted scoring opportunity, and at the end of the 4th quarter is obviously the end of the game - if a team is behind, it needs to score.
With this in mind, it’s not uncommon to see teams hurrying to score late in each half before the clock runs out on them. It’s more common in the 4th quarter - some teams choose not to risk going balls-out to score late in the first half, as bad things can happen. (see this thread for that discussion)
Anyway, the 2-minute warning tends to work in the offense’s favor, as it gives them a free additional time-out if they manage the clock properly. My thinking is that the league likes this, as it tends to promote drama in the form of giving last-minute desperation drives a better chance at success.
It may be a holdover from some old rule, or it may have been put in specifically for the reason I’m suggesting - I’m not sure. Or, I could be completely wrong in my speculation. 
I suppose it should be noted the college football does not have a 2-minute warning - it’s only used in the NFL. (Don’t know whether the XFL will be using it or not.)
…give whoever is broadcasting the game another commercial slot to sell.
Zev Steinhardt
The two-minute warning has its basis in the early days of pro football. At that time, the scoreboard clock wasn’t official; time was kept by an offical on the field. As such, the two usually out of synch. The referee gave signals to the scoreboard operator to keep up, but the teams couldn’t depend on what was on the scoreboard. So they had a two-minute warning to make sure the teams knew they had only two minutes left. It’d be a mess if you thought you had an extra 30 seconds to score, and discovered time ran out.
When TV came in, it became a convenient place for a commercial break. Also, it had become ingrained in strategy. When they went to having the scoreboard clock as the official time (I believe first in the AFL in 1960, and in the NFL after the merger), the two-minute warning was kept.
Besides what has mentioned before, the two minute warning also serves to notify the teams that there are new rules in effect, such as fumble recoveries and penalties.
However, college football has gotten along for 100 years without a two-minute warning.