I know what you mean!! I saw something on TV once about how peaches and such get mealy - it has to do with the temperature they are exposed to while in transport or at the stores. I don't remember, though, if they are kept too cold, frozen (accidentally) or what. But it's definitely nothing that you did after you got them home - and it's definitely not that they are overripe. If I find more info, I'll come back and share a link!
ETA: My memory isn't half bad!! Here's a link (scroll way down for mealy peach info), plus an excerpt:
http://www.producepete.com/shows/treeripepeaches.html
QUOTE:
"Never place firm tree fruit in the refrigerator as this will halt the ripening process and may make the fruit mealy, dry and tasteless. Never store tree fruit in a plastic bag as this may hasten decay. Also, keep tree fruit away from direct sunlight as extreme heat will damage the fruit. When the fruit is ripe and you can keep it in the refrigerator for a week or so. You can tell when peaches and nectarines become really ripe when they become aromatic and give to gentle palm pressure. "
ETA: My memory isn't half bad!! Here's a link (scroll way down for mealy peach info), plus an excerpt:
http://www.producepete.com/shows/treeripepeaches.html
QUOTE:
"Never place firm tree fruit in the refrigerator as this will halt the ripening process and may make the fruit mealy, dry and tasteless. Never store tree fruit in a plastic bag as this may hasten decay. Also, keep tree fruit away from direct sunlight as extreme heat will damage the fruit. When the fruit is ripe and you can keep it in the refrigerator for a week or so. You can tell when peaches and nectarines become really ripe when they become aromatic and give to gentle palm pressure. "