Here's an anecdote, for what it's worth.
I do a lot of doodling boxes-and-arrows stuff, pseudo-UML, half-assed flow-charts, etc., when working on ideas. For some strange (and largely irrelevant) reason, I'm really picky about the pencils I use. And my favorite ones have apparently gone out of production. So last week, I order two new high-end mechanical drafting pencils from Amazon. They show up, I like them right away, so I order 5 more.
The package arrives, and there are only 3 pencils. From what I can tell, they were loosely slopped in along with the book that in the same order and the packaging was loose enough that I'm guessing the other 2 actually fell out.
I login to Amazon.com (this was on Friday), report the 2 missing pencils, and wait to see what happens.
A few hours later I get a notice that a replacement package is 5 pencils is being overnighted to me. Note that only two were lost from the original package.
For all the grief Amazon gets, at times their customer service can be pretty damn good.
Wal-Mart, OTOH, to me, just "feels" like a place to get mostly cheap crap, sold by underpaid employees with surly attitudes. I don't even think of walmart.com as a place to shop online. They're so far off my radar that they might as well not have e-commerce.
The question then, to me, is how many people have a world view like mine? And if the answer is a large number, how does Wal-Mart get people to consider them at all? Leveraging the hybrid "click and mortar" thing sounds like a good start, but I'm wondering if it will be enough.