Power ratings on notebook cards: an indicator of ability?

I'd like to buy a wireless card for a notebook. In looking at the specifications of the various cards, e.g. at NewEgg's web site, I see some specifications include transmission power ratings.

For example:

The ENCORE ENPWI-N 802.11n Wireless CardBus Adapter has
Transmitted Power:
17dBm typically @ 802.11b
13dBm typically @ 802.11g
13dBm typically @ 802.11n

and the LINKSYS WPC100 RangePlus Wireless Notebook Adapter has
Transmitted Power:
18dBm ~ 19 dBm, ±1.5 dBm @ 802.11b
15dBm ~ 17 dBm, ±1.5 dBm @ 802.11g
9dBm ~ 17 dBm, ±1.5 dBm @ 802.11n

It appears the way the statistics are presented may be a distinction without a difference, e.g. "13dBm typically" vs. "9dBm ~ 17 dBm". They both may have the same power transmission capability and the manufacturer simply selected a standard to report out. (I think the link to the FCC information on this bulletin board was really helpful!)

My question is, are some cards more powerful in their transmission vs. others? If so, is the power transmission a criteria one should consider when trying to buy a card that will have the best performance. I realize there are a host of other variables that affect the actual throughput performance, but it seems to me if one card can transmit with more power than another, then certain environmental hindrances might be better overcome.