Occasionally, somebody will notice that upon installing a program, it managed to pin itself to the taskbar. But just like there is no
PinToStartMenu function, there is also no
PinToTaskbar function, and for the same reason: Because applications would abuse it and auto-pin themselves because they are so awesome, and so that the developer could get a nice bonus.
In spite of these roadblocks, some applications manage to pin themselves to the taskbar anyway, typically by programmatically driving the shortcut context menu. The developer then collects their bonus and goes out and gets drunk.
There is no real way of blocking this behavior other than giving guidance not to do that. Customers who complain to the vendors about their presumptiveness may help. Scornful looks and ignoring them when they walk by the lunch table looking for a place to sit may also work. (But since they're drunk, they may not care.)