Why don't you get a +1 ability score per level?

[Kavon]

Do you realize how many things in the game can be solved with a "minimal amount of bookkeeping"? Now, solve all of them, and what do you get? A whole lot of bookkeeping!

Sure, for any particular single issue, the bookkeeping isn't a major burden. So, for your game at home, go ahead. But as a policy for designers, reducing bookkeeping by shaving here or there makes sense.

Sure, let's never try to change something to fit our own style of gaming because it starts to bog down the game if you do it too much.. Like I said, depends on how you like to handle things.
We're talking about a really insignificant piece of bookkeeping here. Something that only comes up when a character levels up (which, let's be honest here, in 13th Age only happens 9 times).

I understand your point when considering it from a designer's point of view, but there's nothing stopping anyone from making it an optional method of handling it(which, again, they seem to be quite open to in 13th Age, with the casual notes on the sides)

 

[Tharian]

[MENTION=43019]keterys[/MENTION] is spot on from my reading of the book as well. It aligns very nicely with the tiers of play already created. I find it reminiscint of the adds made to characters in D&D4e when moving to Paragon or Epic tiers.

 

[Jhaelen]

As far as book keeping goes, it is just one more box to check off as you go up in level, the players are already doing that. You can just use the box they have for the normal gain at 4,7, and 10.

This!

I really like this idea. It makes choosing stat arrays with one or more odd stats a lot more attractive. I've found that players otherwise vastly prefer having even stats, at least for their primary and secondary stats - which also happen to be the ones that are (almost) exclusively raised.