I'm not sure what people were expecting with the Apple Watch. You can get the aluminum models for $300 (38mm)/$350 (42mm), the stainless steel models for $500 (38mm)/$550 (42mm), (black SS) $600 (38mm)/$650 (42mm), or full bling starting at $10k, plus the cost of the band you select. That basically makes it a convenience accessory accessible to anyone using a newer iPhone, and who wants to leave their iPhone in their pocket or bag during most of the day, but not miss out on notifications or calls, while still being able to keep up on breaking news, messages, email, calendar events, check the weather, track their health, query Siri for Internet info, check the time, and who knows what else once developers jump fully into the product line.
Sure, your iPhone can do all this better, but not more conveniently. You can now create a subset of all the emails and notifications you want to know about instantly, vice the barrage you regularly allow on your iPhone just because you can. How often do you get sucked into doing more than you intended when you picked up the iPhone? The Apple Watch is for the important-to-you events you simply don't want to miss out on, but only take up a few seconds of your time to do so.
For me, that's very cool. I'm retired, so my iPhone now sits in the charging dock most of the day while I go about my interests around the house, remaining fully online for the shorter list of key interests that I don't want to miss out on (including calls from my spouse), while retaining the option to get my iPhone for items that actually require the larger screen and keyboard, which is seldom in my case. For Internet browsing around the house, I pick up my iPad off the coffee table. My iPhone now only goes in my pocket when I leave the house and want to remain online, otherwise it can stay home while I walk the dog, instantly updating me the moment I return within WiFi range of my iPhone.
For those not retired, you can follow the same approach at work, configuring your Apple Watch to limit getting your attention from those apps that are critical to your day, leaving the rest waiting for you on your iPhone for a quiet moment. Your social apps can remain actively updating on your iPhone, while not bothering you on your watch. Only my VIP configured email gets transferred to my watch now, everything else stays in my InBox until I choose to look through it.
Yes, the Apple Watch isn't a necessity, any more than the iPhone is, but it is a big convenience. As others online have already stated, your Mac/PC is for when you have hours to spend doing something, the iPhone is for when you only want to spend minutes doing something and you're mobile, and the Apple Watch is for when you're only willing to allow a few seconds of your attention. That works great for me.