I've always viewed personas as something similar to a user log-in on a computer. For example, when I turn on my PC (real world, the one I'm typing on right now), my computer automatically logs me in as my User account. It does this automatically, because there aren't any other accounts registered on the computer, but if there were, it would ask me to pick an account. Most computers do this, and even if it doesn't ask which user you are, it is usually because it is using some sort of default, at the very least filing the activity under the default Admin user account.
In the Shadowrun setting, I imagine this works in a similar fashion, your primary device (commlink, cyberdeck, etc), is probably set up to use some sort of default account based on how you set it up when you bought it. When you turn on these devices, it logs you in and connects to the Matrix. The rules do mention several times in several places that Personas are how a user interacts with the Matrix. "When a person uses a device to connect to the Matrix, the device’s icon is subsumed by the persona’s icon..." (Page 235 Core Rulebook).
Now, some devices might be able to generate more than one persona, through the use of Agents, which results in more than one 'user' being active at once. And some devices won't create their own personas because they function in a supplementary role (devices attached to a PAN).
The items like the toaster and the coffee maker in the OP are examples of this last thing. They might have access to receive information from the Matrix, they might even have displays that allow a user to interact, but they aren't really the device that accesses the Matrix. That responsibility belongs to the Commlink of the user. You can use those devices or issue them commands in much the same way you might interact with the Matrix using AR gloves and goggles for a display.