Yeah, weapon bonuses tend to follow the number of attacks a full BAB weapon-type characters get. I don't need a chart to understand that. You could just as easily divide 20 by 5 (+1@4,+2@8,+3@12,+4@16,+5@20), and run with that, too. It doesn't have to be set in stone.
However, if they are supposed to find any of this as gear, versus they are expected to purchase everything at full price, then you have to give it to the NPC's/enemies... which throws off NPC wealth, which raises the CR, which means more XP, and faster level progression, and higher expected character WBL... it's a stupid feedback loop of stupidness.
Just go with what is fun. Don't let any of your boys fall behind where it isn't fun anymore. Pretty simple actually.
The wealth provided by adventure paths is based on the expectation that you will keep some of the items, use others immediately but then sell them later, sell some items at half price without ever using them, buy some items at full price, craft some items at half price, fail to find some hidden treasures, use some consumables, pick up some consumables but never use them, lose a character and then have to deal with what happens with that character's loot versus the items the replacement character needs...
It's not an exact science.
The wealth provided by adventure paths is based on the expectation that you will keep some of the items, use others immediately but then sell them later, sell some items at half price without ever using them, buy some items at full price, craft some items at half price, fail to find some hidden treasures, use some consumables, pick up some consumables but never use them, lose a character and then have to deal with what happens with that character's loot versus the items the replacement character needs...
It's not an exact science.
Considering all this, APs are pretty good at landing somewhere around where your WBL tends to be though occasionally the plot leaves you pretty dry for loot. I.E when you cant sell stuff but have stuff you cant really use.