Couldn't this approach be abused?

This does not seem to be necessary if your system is properly deployed and uses enterprise level encryption/authentcation. Jsut another gimmick to scare people out of their money...

What's so wrong with Wi-Fi? I mean it uses similar techniques as VPNs to perform strong authentication and encryption. So if Wi-Fi is so unsecured, then how come we have come to trust so much VPNs? A company's VPN gateway faces millions of potential hackers over the Internet, whereas a wireless network will only face a handful (if at that) of hackers near their vicinity. One may say "but Internet traffic is much harder to capture in promiscuous mode than wireless traffic". Right, so just go to any coffee shop / hotel / airport and you can easily capture VPN traffic over the air. And break it if it's so unsecured! Or maybe some are simply trying to exploit other's insecurities…

Wouldn't this approach also tend to block the use of cellphones inside the business location? That seems to point towards better use of encryption and suthenication and away from this methodology.

I've used another approach effectively. Place an additional protection AP on a nearby channel in the area to be guarded, say channel 3 or 4 to protect channels 1 and 6. For an outdoor area, a directional antenna my be best so as not to interfere with the indoor areas that do require good coverage. Direct these "protection" AP's clients to a benign banner page or black hole. Then take the APs that are leaking into the outdoor areas and lock up their fallback rates so that clients can not associate at lower speeds. Facing interference outdoors from the protection APs, a rogue client will attempt to fall back to a lower speed, but will be denied by your higher speed only AP settings.

This offers substantially less 'security' than good-old WPA.