It is FSX's fault. The sim wasn't designed to handle complex flight dynamics like VTOL. You can only go so far to get it to look kind of right, but it's never ideal. Don't blame Razbam, it's the limitations of the platform. It can't and never has done well with high-performance aircraft, VTOL, thrust vectoring...anything extreme. Only way for developers to work around it is to write their own flight control program to bypass the sim's (similar to what VRS is doing).
EDIT:
On the subject of DCS, our development team has (on the side) messed with VTOL capability of a jet aircraft using an external flight model, and it worked absolutely brilliantly. Just as you'd expect a real VTOL aircraft to perform. Thing is, there is no limit to what flight model you want to make in DCS - it's an un-restricted platform. It's all up to the developer how detailed they want to make the flight dynamics.