Reading through some archived posts about the nature of wood expansion I gather that most wood expands mostly width wise and very little lengthwise. One poster stated that hardwood expands mostly in the direction of the tongue. This would mean that the wood expands towards the stapled side of the board and away from the groove, hence the practice of starting rooms wider than 20 feet in the middle and working out towards the walls. Is this accurate?
Also, ever since getting into the flooring business a few months ago I find myself checking out floors wherever I go. The one thing that really sticks out to me is the gap (or lack of gap) between hardwood and ceramic tile, regardless if the wood is parallel or perpendicular to the tile. From what I have read throughout this forum it is proper to leave at least a grout line width between ceramic and wood and fill with colour matched caulking. EVERY floor I have seen is butted directly up against tile with no expansion gap what so ever. Many of these floors seem to have been in place for quite some time with no ill effects. How extreme do changes in relative humidity have to be to make this lack of gap an issue?

To be honest with you I don't know. I leave the spacing for a safety measure.

If you are looking at commercial floors or in shopping malls, those floors are not usually installed very tight to start with and the environment does not change as dramatically like when a homeowner wants to air out the house in the summertime.

The gap is your insurance