Of course, you can ask your question anywhere on the blockchain, however, one of the main differences is the interface and the features you'll be able to build on top of Quello when compared to a community.

Communities at blockchain level are currently one size fits all, which is great and extremely valuable for bringing various topics alive however I'm not sure a community alone would be enough to bring questions and answer enthusiasts (Quora, Yahoo, other Q&A sites) to Hive as they would expect a dedicated interface with functionality focussed on asking and answering questions. Having a site focussed on Q&A helps to narrow an audience and filter out other noise on Hive that wouldn't be useful when trying to onboard the users I mentioned previously.

There is a much longer answer to this, where we can dive deeper into features, onboarding, retention, however, thought it might be useful to keep it short 👍