Isn't that kind of an irrelevant distinction if Echo is mainly designed around that one feature/gateway to features?

Have you used an Echo? The product and the human-interaction agent are clearly intended to be the one and the same.

You don't buy an Echo that comes with Alexa; Alexa is the whole point of the Echo.

You could essentially do the same through Siri - in either event, the separation of the entities still makes sense.

I don't personally understand the need to humanize interactive services and apps, but I guess Siri made that appealing.

Because you're communicating with a device that refers to itself in the first person. Anthropomorphization is inevitable. It's not like this is new, either. 2001 comes to mind immediately, but I'm sure there are plenty of examples that predate HAL.

The different names seemed odd to me at first but it's not that big of a deal. I presume Amazon thought about this.

An slways-on, self contained voice controlled speaker is an entirely different experience than Siri.