The point of a patent is to gain a limited monopoly on an invention in the marketplace. People invent things, companies do not.
The fact remains that unless the employee is sharp witted on legal matters, the employer is going to unconscionably screw them.
Sadly, the employee must remain vigilant and not agree to such restrictive nonsense. (and not just in terms of purported ownership, but also in terms of arbitration). Friends don't let friends use the government to solve their problems.
We're in an era of reputation (look at LinkedIN, and Klout), and the patent system will inevitably revisit the concept of reputation inadvertently.
Depending on what political and philosophical angle you are coming from, the whole patent system looks like pure evil, or good in a "screw them before they screw us" sort of way.
Without artificial monopolies, companies would have to depend purely on their product quality, source authenticity, and reputation.
Employees should not also be monopolies.