That's Amazon Prime. Non-prime purchases are, in my experience, deliberately delayed. I'm two days from their New Jersey warehouse, and my last three purchases were all delivered in 7 business days or longer. All items were fulfilled by Amazon.
> waiting a couple weeks for an eBay shipment
As a former seller on ebay (20-30 items a month), getting things out on time is a priority for lots of people. Especially sellers shipping a lot of packages. Namely, because you want those good ratings from customers. Get a bunch of neutral/bad reviews because of shipping, and your sales will plummet.
A lot of eBay sellers actually source from Walmart. I have. I works pretty great... sometimes. Just gotta be quick about getting their clearance items or pricing mistakes.
However, this:
> And after you're accustomed to 1-2 day shipping from Amazon, waiting a couple weeks for an eBay shipment is a non-starter.
Ignores the fact that (at least for the stuff I buy), you can usually get 2 day shipping from eBay sellers. The only time I have to wait more than a few days when ordering on eBay is if what I'm buying is rare enough that I have to buy from an out-of-country supplier -- and those things are rarely or never found on Amazon anyway.
I like eBay well enough and I have my quibbles with Amazon (especially the marketplace) but they definitely have the one-click-and-you-have-it-tomorrow game nailed.
I was selling off some old PC Magazines and Bytes from when I was a teenager and was surprised that magazines aren't supposed to be shipped via media mail since they've got advertisements in them.
Priority Mail != Media Mail
There's no question about that.
But personally, this isn't a big deal for me. That's one of the reasons that I've really taken to "Amazon Day" for shipping -- I rarely need something the next day, and am entirely happy to wait up to a week for my Amazon order in exchange for only having one shipment per week.
My cutoff for "too long" tends to be a week or two, depending.