Worlds is the first qualifying event for the Olympics. It works in a similar way to how spots are qualified for the next year's Worlds:
* For countries with two or more skaters - to get or retain three slots, the combined placements of the top two cannot exceed 13. For example, at last year's Worlds, Chan was first and Reynolds 12th. Together, this was just good enough to qualify a third spot for Canada. To retain two spots, the combined placements of the top two cannot exceed 28. Lower-ranked skaters get no worse than 18 in this calculation, so it's not that hard to do, but it's not automatic, either; last year, Gachinski and Voronov were 17th and 18th, and Russia went down to one men's spot.
* For countries with a single skater - to qualify three slots, that skater needs to finish in the top 2 (I think). To qualify two, that skater needs to finish in the top ten. For instance, at 2009 Worlds, Denis Ten finished in the top 10, qualifying two slots for Kazakhstan for the Olympics; Abzal Rakimgaliev was the beneficiary of the second spot. OTOH, Carolina Kostner finished outside the top ten, which essentially meant that Valentina Marchei was out of luck for the next season.
In order to qualify a single entry to the Olympics, I think it's something like top 20 or so.
There are some Olympic slots left open after Worlds. For countries which did not qualify a single entry to the Olympics at the previous season's Worlds, a fall senior B is the qualifying event for the Olympics. This is the last chance to qualify Olympic entries, cannot be used if a country has already qualified a spot in that discipline, and can only be used to qualify one spot per discipline. In 2009-10, The Nebelhorn Trophy served as that event, and this was where Stephane Lambiel got his Olympic ticket.
The Olympics are not a test event and promising young skaters are not entitled to a shot at competing there. You have to qualify the spots and you have to be among the best from your own country. We've seen more accomplished skaters than some of the young Russian ladies miss out, and while it's unfortunate, it's not unfair. Everyone knows the qualifying procedure and it's up to the skaters to perform well enough to go.