@elmer: Not "all?". When finding a USB/Serial adapter it is important to see what chipset it uses and if it handles both hardware and software handshaking. Once you find one that meets those criteria then you have found a rock solid adapter. USBG-232 has been rock solid for years. http://www.usbgear.com/usbg-232.html
The support and development folks have been at odds for several years now over this. Support still encourages users to install the converter instead of using USB/(Activesync/WMDM) because it is an instant usable connection and simplifies user life.
Even with perfectly good USB/Serial adapters, there's still the chance that the thing may fail spectacularly. I've seen some devices (no names here, to protect the guilty) that draw small amounts of current off the control signals; no big deal with a real serial port, but enough to make the chip in the adapter go bananas. For extra fun, make sure that the device doesn't draw current continuously and that the peak is borderline.