Daffs are really tough, so I doubt it would hurt, and I admit I have replanted immediately with no problems. Most spring flowering bulbs prefer to be dry during summer dormancy, but some are more demanding of it than others (like Tulips and Hyacinths), and Daffodils are among the least fussy. Moisture during that time can cause rot issues though, so if you happen to get a wet summer, it could do them in. Not nitpicking at all, an excellent question! I'm the same way, if I know why it's a general rule, I'm more likely to remember it (and abide by it).
