Pushing the dota 2 release date to the year 2012 could have to possibly work on the closed beta. After that, they then do the open beta. They then let everyone play it for free. Somewhere in the mid year of 2012, when everyone is addicted to it, they will begin to charge some cash.
If you want also want to know that this delay could as well be a marketing gimmick, then try to remember what happened to SCII. The same is also likely to happen with DIII. It is this kind of marketing strategy which allows them to publicize the game before releasing it to the anticipating fans. This enables them to make quick sales and fast money which they would use to reinvest in the production of the next version.
In business, it is all about staying relevant to the market. It is the only way you can keep your base intact. You have to offer the best of your ability. They are therefore trying to achieve this kind of relevance by taking quality time in the preparation of the game to avoid disappointing their fans.
You will also note that beyond the tweaking of figures, there is more of balancing and testing. This takes some time to achieve. So as time elapses, valve will unleash one kind of a masterpiece that has never been seen before. It is quite unwise to rush up things and in the process end up with a low quality product.
An important consideration is that the whole of this is primarily still a figure in this game code. When it takes them long to make up the missing block, it becomes better. When fitting the loopholes, they still require to check out the game is properly functioning and working. These already points out how balancing and tweaking are slightly similar.
The process of making the heroes is the most hectic part of the software construction. You should practice patience to have well made heroes. The appearance should be simple and neat. Primarily, this game is meant for entertainment purposes and you will come to admit it that to make good entertainment, you need quality time. You will need to check and counter check the loopholes so as to have a fine final product.
In marketing, hyping the game is part of the entire commercial strategy. So from that point of view, it is intended to create high demand of the commodity through anxiety and speculation. The result of it is quick money through fast sales of the software. They then use part of the earned profits in reinvesting in the subsequently coming version of the same. It helps them remain relevant to the industry.
If you want to ascertain that this delay is actually a marketing gimmick, then remember what happened to SCII. The same is also likely to happen with DIII. They might have also pushed the dota 2 release date to this year (2012) as to work on the closed beta.