However, the chances of any of us being out in the elements, to THAT extreme, are pretty remote. Face it, we're essentially wimps, and enjoy our AC.
That said, YES, the SAI synthetic stocks are a bit light in the foregrips, and are subject to some flexing... which means a bit less accuracy. Several folks on the boards do work related to stiffening them up. I handled one today which had been very professionally done, and it was a dramatic improvement.
So, while wood may swell in the summer, and could feasibly impinge on some moving parts of the rifle, the chances of that are rather low. Out of the box the SAI stock is good, but can be made better.
In the end it gets down to what you want to do with the rifle, what you want to spend, and what your tastes are.
BTW, remember that these rifles can outshoot most of us right out of the box. Spending a lot on accurizing the gun is best done AFTER you're shot it multiple times, and have determined that accurizing is warranted.