It's all fun stuff and of some usefulness to me personally, but I don't think much of anything I've done has any professional applicability; other than generalized familiarity with electronics and components I wouldn't feel comfortable producing a real product.
Are there actually consumer electronics out there that are just arduino examples glued together?
A lot of the existing power-switches that can be toggled with an app / radio-button are little more than an ESP8266 and a relay. The sonoff-line of smart-switches would be the obvious example.
Sonoff also make and sell RF<->WiFi bridges, but I guess the target market is already hackers rather than consumers for things like that.
Otherwise I've seen a few wifi-controllable LED-strips, and similar things that I'm pretty sure are identical in terms of hardware to what I've built. You can see some crowdfunded projects are just scaled-up home-toys too.
I'm struggling to think of better examples, but I'm sure they exist! In terms of product though it's interesting to evolve something from a bundle of junk loosely coupled to being a thing in a pretty case which can be enjoyed by others. I setup a trivial display to show tram-departures from outside my house, which the whole family uses now and loves. It went from a cardboard-box with a pile of stuff in it to a 3d-printed display, and then later I added the ability for it to be controlled via a HTTP-server, running as an Access-Point when it was initially setup. The whole thing became very very user-friendly. (But at the same time the only real user is ourselves, and trying to sell it would be a bit difficult.)
The Arduino IDE is also compatible with various other microcontrollers, including the STM32 family which are extremely widely used in production electronics. Typically their production code isn't written with the Arduino tools but you can most certainly prototype with it.
Some of the newer ones can trace their lineage pretty directly to Arduino clones running TMK/QMK firmwares. The commercial version is usually going to cut out as much of the Arduino bits as possible and go for a soldered on microcontroller once you're building for sale.
You'll find AVR chips controlling many, many devices in the wild. My Lulzbot 3d printer uses an ATMega for instance.
I figured I'd either learn android-development, or hardware-stuff. Bought an Arduino kit and never looked back. In my limited experience people dabble at such things then move on, or give it up entirely there isn't too much of a middle-ground.
I still dabble with ESP8266 things two years later; most recently I hooked up a simple 433Mhz radio-receiver to a board, and wrote some code to receive/understand/decode the radio-broadcasts a cheap off-the-shelf wireless temperature/humidity-sensor transmits. This allows me to log the temperature/humidity of our sauna.
Usually I'd wire up a sensor of my own, but I figured it would be less-risky to use an off-the-shelf sensor/transmitter. The idea of mixing steamy saunas with a USB-PSU was a dangerous one, and I even balked at using a rechargeable battery.
There aren't many things I buy for my hobby/practice, just random sensors, or accessories. Most of the time I just order them from AliExpress and take the time-hit waiting for them to arrive.