ASICMINER's next generation chips will be out by November... do you honestly think any of these IPOs will produce functional products by then? We don't know the specs of the next AM chips... but there is every reason to assume they will be in line with the specs these other companies are promising, if not superior.
The primary difference is that ASICMINER has proven that they can deliver.
Great so... lets invest in an unknown. I don't doubt they'll come up with something awesome, but they also have a glass ceiling in the percentage of network hash rate they can take. They've currently got 12% of network hash rate, so they could double that, but not really any more than double... that's their major class ceiling. Whereas ActM can increase their hashrate by a few hundred times, plus hardware sales.
Their franchising plans means no hashrate glass ceiling. Plus hardware sales.