According to Wikipedia, it is one and the same device:
The HTC Sensation is a smartphone designed and manufactured by HTC Corporation that runs the Android 2.3 Gingerbread software stock. Officially announced by HTC on April 12, 2011, the HTC Sensation was launched by Vodafone in key European markets including the United Kingdom on May 19, 2011 and by T-Mobile in the United States on June 12, 2011 (marketed as the HTC Sensation 4G)
I'd suggest making the "4g" a synonym for confused US citizens :)
Question is whether to include the htc-sensation-xe (× 8) as well, as the above quote continues:
It was the first official HTC phone to support the HTC Sense 3.0 user interface. At the time of its release, the Sensation XE was the world's fastest Android phone.
(emphasis again mine)
Like the Sensation XL, the XE ("Extended Edition") is a variant of the Sensation. Differences of the XE to the base model, according to Wikipedia, seem to be a faster CPU (1.5 instead of 1.2 GHz) and a bigger battery (1730 mAh instead of 1520 mAh) only -- which for our site I see not justifying a separate tag.
For confused users again,
htc-sensation-xe could be converted into a synonym.