Shopping for tubes online.....I am seeing descriptions that indicate the same tubes are suitable for both sizes..........any validity to this?

Yes, The sizes are so close they are interchangeable. I hink you would be hard pressed to find a tube labeled as 27" only.

...And if you do, you can ignore that because a 27" tube will work fine in a 700c rim.

The width is more important. If you try stuffing a ~40mm tube in a 23mm tire you will have problems. +/- 5mm is always safe though.

Don't confuse the fact that the same tubes fit both 700c and 27" tires by assuming the two tire sizes fit the same rim. They don't.

+1

yup. tubes are fine (if you have the width within reasonable range) and match the proper valve type. Schraeder valves are more common on 27" rims and presta are more common on 700c road bike wheels.
as HillRider notes, tires are not AT ALL forgiving for different sizes, because their fit on the rim depends on a basically unstretchable bead.

A 27x1 1/4 tube is going to be a bit "FAT" to stuff into a 700/23, would probably be OK in 700/28 -700/32. A 700/23 tube in a 27x1 1/4 may be a bit tough on the tube...tried that once last year and it blew out on me in under 2 miles, but not sure if it was the smallish tube, the old tire or the hookless rim that caused the fail.

700c and 27' tubes of the same width (not tires, as stated above) are not only interchangeable, they're often identical. Makers mold the same tube and mark the box either 27" or 700c, (or sometimes both) according to the client's request. So it's the same tube, just a different box.

The 27's I can buy at WalMart appear considerably thicker than the 700C's X 25mm I get elsewhere. Would the 27's therefore be more puncture resistant?

Only very marginally so, for those tiny shards of glass too small to go through the thicker wall. IME these are extremely rare, so I doubt you'll see fewer flats.

OTOH the thicker the wall the slower the natural bleed, or pressure loss over time. This will reduce the frequency of needing to top off somewhat. I only ride clinchers for commuting, and use the largest tube that fits for this very reason. Less stretch to fill the tire, means thicker walls and slower pressure bleed. I get by topping off only once a week.

Would anyone like to predict how many responses this simple question will ultimately get?

Somewhere between 27 and 700...Duh...

I don't know why people ask about this, when the percentage difference between 622mm and 630mm is far less than that between width ranges, eg 18-23mm...

I mean, just think about it for a sec. It's rubber.

Okay, you can run into problems if you're trying to stuff too much in there, but if it just needs to stretch a little? Come on, take a guess whether bad things are in store.

Aw heck, it's OK to ask. We were all newbies at some point. I just think it's amusing how everyone likes to answer these questions which are answered completely and resolutely with one response.

Well, the first response might have seemed a bit ambiguous to anyone a bit fuzzy on what the context of 'tubes' signifies : p