Yes, vendors shouldn't do whatever they want, they should stick to the spec. In this case, the spec allows any rendering for select elements which allows the user to choose from a list of options. Using a different rendering from other browser does not violate the spec.
I've always felt like this was a major shortcoming of the specification. Inputs should have some consistent visual specification along with support for a well-defined set of styling options. We go through all of these gyrations precisely because the spec. doesn't define standard behavior. The differences in color, size, and shape from platform to platform (and browser to browser) can be very problematic for anyone trying to make the web beautiful.
The other side of the argument is that it is beneficial that browsers determine how such elements work. If they did not, millions of mobile users would be struggling with tiny but beautifully rendered UI elements.
