Many small companies and even individual bidders are on the list because there are hundreds of small area licenses up for grabs, many of which will probably sell cheap. A single 700MHz 6MHz channel may be plenty for a small WISP to provide much more reliable - not to mention mobile - broadband service than they can provide today with their 5GHz unlicensed Canopy or Alvarion gear. These small operators are crowding each other in the major unlicensed bands in urban areas, and they'd love nothing more than a piece of spectrum to call their own.
One of the reasons you see so many Incomplete entries is that many of these bidders don't plan on making a bid in this round because of the minimum bids and reserve prices. They're hoping that a bunch of these licenses will not meet minimums and won't be awarded, and there will be a new auction (Auction 76) later in the year, which will be their chance to pick up some spectrum very cheap... or so some of them hope. The trick is that they can't bid in the later auction without having gotten on the list for this one. I'm sure others are on the list for other reasons.
Speaking of crowding, this also touches on why we need licensed bands. Protocols like 802.11 (Wi-Fi) are great for unlicensed bands because they have congestion-avoidance mechanisms, while 802.16 (WiMax) only really works when you can synchronize the transmissions from all the towers - impossible in an unlicensed band. Wi-Fi is great but it will never be able to provide the same level of Quality of Service (particularly controlled latency and jitter) that WiMax can give you.