Any valid ranking system has to allow for the possibility of someone being the #1 ranked player without holding any slam singles titles. It's happened before. Tracy Austin held #1 without a slam title and only 2 slam semis in late 1980, over Chris Evert who had 2. Steffi Graf held #1 in the spring of 1991 with no slams, and did it again in the spring of 1995, in both cases over a player that held 2 slams (Seles and Sanchez).
For Davenport to finish at #1 this year, she will most likely have to win the Tour Championships, which is the 5th biggest tournament, and unofficial "5th slam". Last year (and throughout her reign this year), Hingis also had the "5th slam" among her titles. As did Austin.
The slams count twice a Tier I. Even more over a Tier II. Which means that a player winning no slams has to win at least two titles for every slam another wins. That also consumes 2 slots of their best 17, leaving them less space. If the slam winner does anything in that extra tourney, she's ahead. The non-slam-winner has to be exceptionally dominant in her other events to make up that ground. Davenport has. Remember when Hingis went 19-1 during the fall indoor season, one of the greatest finishes in tour history? If Davenport wins the Championships, she's 20-0 indoors this year.
To put it into another perspective, how many individual decathalon events do you need to win to get the gold medal? Answer: none. By doing better than your opponents over the course of all of the events, you get the gold. Even without winning any dividual events. Sure, if one guy wins, say, 4 events, he and his fans will complain. But the system is the same for everyone, and set up in advance. If there are no complaints when it's implemented, there should be none when it doesn't produce the results someone wants, or expects, without looking at the whole picture.
What gets me with the tennis media is the ones who cry out to the WTA to "fix the system" to meet the expectations they have after watching only 4 tournaments a year. Where are their suggestions? There aren't any forthcoming, because any ranking system can produce results like this, and many have glaring problems of their own.
People are bitching that the slams don't get enough emphasis, because Venus didn't get #1, then Jen didn't get it soon enough. 2 years ago, people were bitching that the slam emphasis was too high, because Stevenson and Lucic were held aloft in the rankings based almost exclusively on their Wimbledon results. It's the same ranking system. So which is it? Does it give the slams too much or too little emphasis? That there have been complaints in both directions indicates it's doing a pretty good job. If Jen holds #1 she deserves it. If Lindsay takes it, she deserves it. It's not easy to pile up points at regular events, especially if other top players and their quality points aren't present. If someone can do it under those circumstances, more power to them.