Hello DELIVERYMAN3,
6 is a key number because of a TD, or two field goals. It may not happen that often, but placekickers at times do miss the extra point, and there are many times where teams lead by only two field goals. 10 is the highest I will go, either buying up or down the half point. And for 4, well I think my point will be best illustrated with this example-I am sure that you have seen these types of scores a lot before.
3-I read an article where 15% of games land on this number;10-7,20-17,27-24
4-I have seen these types of finals before;24-20,17-14,28-24
6-with the aforementioned reason;23-17,26-20,even scores like 6-0
7-very obvious one with the TD and point after;17-10,14-7,27-20
10-the highest I will go;20-10,27-17,30-20
Take a look at the data (scores going back for 10 years at least) and you will probably find a lot of scores like this being the final. And every time you bought that half point it either turned a loss into a push and a push into a win, which makes a very big difference over the long haul. It is these certain numbers that have the biggest impact because with the scoring system these are the incremental amounts the scores go by (safety's and two-point conversions before the game starts are impossible to account for).
Now that I am on the subject, I would just like to bring something else up related to this. Another poster here on Pregame, VEGASBUTCHER, brilliant person, mentioned he does not or rarely buys half points. His reasoning is that you need to increase your winning percentage in the 54%-55% range to break even when laying vigorish of -120 to -125. This may be true, but I have two perspectives against that. The first one being that buying the hooks on these games is a general rule of thumb. If you don't like it or doesn't work for you I can appreciate that, but as a handicapper I will always be persistent on this philosophy. My second point is that if you can't make this winning percentage buying the half point over the long term, then you shouldn't be sports betting or at least find a handicapper who is honest and transparent that can provide you with winning picks.