Yes, there is a world of misinformation out there.
Let's start by breaking down the two different groups by catagory.
The 2.4 gHz frequency (ISM) is used by both the 802.11b and 802.11g equipment. The range these devices actually have can be mathematically predicted. For example, if there is nothing blocking the signal, an access point with the standard "rubber ducky" omni antennas can keep a usable signal with a notebook PCMCIA card (and no external antenna).
Now if you place objects in between the notebook and the access point, the distance diminishes. Metal will usually stop the signal dead as will water. Trees will kill your signal. Concrete will degrade the signal and if the concrete is reinforced with metal, it will kill the signal.
There great thing about RF is that it behaves pretty much in a predictable way. The output power minus the cable loss (if there is cable used) plus the antenna gain is the laws you abide by. The FCC also sets the output power at 1 watt plus 3db of antenna gain. There is a great page with all the calculations here:
However, if you have an area where there is a lot of 2.4 gHz noise (like telephones using the same frequency) both the 802.11b and the 802.11g standard are going to be ruled out.
As to Europe adopting 802.11g, please understand Europe has much different regulations than the US concerning power output levels and the amount of available channels (Europe has less).
On to the 802.11a standard. The range is roughly the sale as 802.11b and 802.11g (with the original antennas) but it is even less tolerant of obstacles. With good LOS, you should be able to use them. Most manufacturers do not make 5 gHz equipment with detachable antennas. Using the correct network design and placing access points exactly where they are needed should allow you to get what your looking for.
