I don't know how happy I would be myself if I had to constantly fight them to get them to do anything reasonable, but if your laptop is a few years old then maybe. I just don't understand how they can say its a couple of days and then go whoops. Likewise how can you estimate delivery a few hours later when a product hasn't even had a shipping label made yet?

It's most likely due to how Dell manufacturing works.

Dell uses a "Just In Time" sourcing model. I'm going to over-simply things, but basically at the time your purchased your laptop, Dell didn't have the memory for it, or the hard disk, or many of the other components they needed to make it. In fact, it's very possibly they hadn't even ordered those components from their manufacturers. When your order comes in, they send a corresponding order off to whoever they are getting the memory from, and another to whoever they are getting the SSD from, etc. That order triggers those parts to be shipped from the manufacturers warehouse (which as luck would have it is located just up the road from the Dell manufacturing facility) to Dell. Dell then assembles these components together, puts it in a box, and ships it off to you.

This is a great model (for Dell, at least) - if everything works as expected. They literally maintain zero inventory of these parts, and don't have to pay their suppliers for them until after you've paid them for your new computer. Parts come in, and within hours the completed laptop might be on the truck headed to the airport. The problem with this model is that it can be a little fragile, in ways that are often not directly in Dell's control. If they place an order for the memory for your laptop, and the supplier doesn't deliver it within 12 hours as they are supposed to, then they obviously can't build your laptop, and the delivery is going to slip. They do have tight integration between their systems and their suppliers, so if they know that 1TB SSD's aren't going to be available they can either stop selling them, quote longer shipping times, or even charge more for them to (to push demand away and towards larger or smaller sizes), but all it takes is for a truck to break down somewhere and they have delays they weren't planning for.

Of course, delays like this can happen in any manufacturing/shipping environment, but the Just-In-Time model increases the risks.

This is one of the advantage of (in geographies that have them - US/Canada and I think the UK) using the Outlet site or the lease-returns refurbished site. The machines ordered from there are actually in-stock, and get to you MUCH quicker.