I don't understand the question, "why not skip 802.11b altogether"?
It was posed as a rhetorical question in that if 802.11a was superior to 802.11b, why even make a dual-band device, that is why not just have a single band 802.11a device and "skip 802.11b altogether". The answer is of course given in the remainder of the paragraph, which basically states that hotspots and such pretty much exclusively use the 2.4GHz band, which excludes 802.11a.
Also, looking down below at the fourth paragraph, "Dual-band hardware can work with either 802.11a or 802.11b/g networks, enabling you to move from an 802.11b/g wireless network at home or at Starbucks to a faster 802.11a office network." So are you saying that Wireless-A is faster than Wireless-G?
Yes. While 802.11a and 802.11g are technically rated for the same speed, since 802.11a has more channels and little if any interference from other devices, in general the speeds will be higher. That is why 802.11a became popular in the corporate environment, while never catching on for the general public. Scott.