According to Android Community, Google has been pulling tethering apps from the Android Market. According to at least one developer who talked to Android Community, Google is citing their distribution agreements with carriers as the reason for removal:

"Google enters into distribution agreements with device manufacturers and Authorized Carriers to place the Market software client application for the Market on Devices. These distribution agreements may require the involuntary removal of Products in violation of the Device manufacturer’s or Authorized Carrier’s terms of service." - Google Developer Distribution Agreement

The agreement is raising "openess" questions for Google. Check the full article at the link below. It's a good read.