Capable is not a guarantee that it will. Especially at a distance. See their disclaimer:
* Maximum wireless signal rate derived from IEEE Standard 802.11a and 802.11g specifications. Actual data throughput will vary. Network conditions and environmental factors, including volume of network traffic, building materials and construction, and network overhead, lower actual data throughput rate. Environmental factors will adversely affect wireless signal range.
But you may wish to check and see if it's connecting with all the enhancements D-Link created for their increased speed. If it is, and it's still not, well, like I said, see the disclaimer.