+1 However I feel they had no choice but to do take this approach because they would have been marketing a non-competitive "smart" speaker otherwise. Pretty sly when you think about it because this melds well with Apple's history in music products and properties. Could this become a smarter speaker with software upgrades? Hope so. But try to use this like an Echo and you may be disappointed. At any rate, I'll be test driving mine on Friday along with a trial Apple Music membership to see how well v1 of this thing really works.
There are a few motivations it seems from this design:
Apple, first and foremost, makes hardware that sells their services. Apple Music, iTunes, iTunes Match. Whatever your choice, all of their hardware is designed to push their services.
They didn't want to make just an AirPlay speaker. There are plenty of those like there are plenty of bluetooth speakers. That would be redundant and the cost they would charge would make it not viable.
They want the product to be able to work on it's own. Yes, you can control what goes to it from a phone, but it's better if you can just tell it what you want.
That requires Siri.
The moment you introduce Siri, you raise expectations for what the product can do "smart"wise. Attaching Siri to a product means the user expects to get smart functionality out of that product.
The problem with Siri, as a previous poster pointed out, is that it is broken up over multiple platforms. iPhone/iPad, Watch, AppleTV, Mac, and now HomePod.
Siri can't possibly operate the same across so many different screens when the output requirement is different. This is where Apple has slowed down their development of Siri. By constantly being forced to adapt to new formats, they haven't taken the time to broaden Siri's capabilities overall.
If you ask Siri something on an iPhone, half the time it will show you a screen. How can that work on a speaker only device? The functionality isn't there yet. In order for that to work, Siri has to be able to audibly answer your question on devices with screens and without. And if there is a screen, it needs to show you something along side that audio, whether that screen is watch sized or iPad sized. That's three different forms of return information from the same service.
My fear is that decent sales will drop HomePod into the AppleTV "hobby" category when people are happy to just control their music and the basics from the speaker. It probably doesn't need to do much more than that. But until Apple figures out a way to serve Siri equally across all devices, the HomePod's smart functionality will be limited to voice commands and not much more.