Being open-source and selling doesn't have to exclude each other. You just have to trust the buyers moral, as in, if they're using it to create things they get paid for, they also pay for a license of your application.
Also, since when has having a closed source ever prevented piracy anyway?
That's a really big if. If it's truly open source then there will also be multiple contributors. Who do you pay? People always say this "open source doesn't mean you're not allowed to sell it!" and that's technically correct, but I don't think this strategy has ever been demonstrated to be economically feasible.
Then again Red Hat's value add is the support. Red Hat's business model is not to rely on its customers' altruism. There are various reasons to dislike such a model, especially for an IDE, not the least of which is that the point of a well-designed IDE like LightTable is that it's easy to use and does not require a support contract. Being a support company creates the conflicting incentive that the software should not be too easy to use. Furthermore, support is not fun; you need to be a big company to earn a significant amount of money, because revenue is directly tied to man hours. Making new and exciting IDEs is fun, and revenue can be more directly tied to the value you produce, rather than the hours you put in.
There are various reasons to dislike such a model, especially for an IDE, not the least of which is that the point of a well-designed IDE like LightTable is that it's easy to use and does not require a support contract.
Lots of BigCo are paranoid about the support contract thing. Sometimes partners and investors want to see support contracts in place as a security blanket. In those cases, the support contract for a "well designed" IDE in your scenario is just free money.
JetBrains seems to do alright selling IDEs. In their case, I think people pay for the value, and they continue to pay for upgrades. Support is through the web, so it fits in with revenue commensurate with value.
Yes, indeed. JetBrains uses a closed source model and that works really well (they have a "lite" open source version, but the version they earn money from is closed source). I'm not saying that you shouldn't do support at all, just that it shouldn't be your primary business model.
Also, since when has having a closed source ever prevented piracy anyway?