Given that HP is buying Palm, maybe they're going to release a slate tablet running webOS instead of Windows 7. Other hardware manufacturers are developing slates running Google Android, but HP could be the only one making a slate running webOS.
If HP wants a product that will effectively compete against the Apple iPad, then a slate running webOS makes more sense. A slate running Windows 7 probably doesn't make sense unless battery life and performance improves significantly. If HP creates a slate tablet running webOS, then battery life and performance should be at the same level as the Apple iPad.