Update: In a statement to USGamer, Epic clarified that it has "not announced plans to stop selling the game" on Steam. "Rocket League remains available for new purchasers on Steam, and long-term plans will be announced in the future," the company added.
Epic's previous statement strongly implied that Rocket League will no longer be available for purchase on Steam once it arrives on the Epic Games Store, but that the Steam version of the game will still be playable and supported for existing owners. So, this updated statement comes across as mere semantics. Psyonix didn't address the Steam version at all in its initial announcement, and Epic used the vaguest wording possible. Given Epic's recent history of exclusivity, I'm willing to bet Rocket League's status on Steam will change in some way at some point in the future. When, how, and indeed if it does remains to be seen.
The latest Epic Games Store exclusive is a whole dang studio. As Epic announced today, it's buying Rocket League creator Psyonix. The acquisition will be finalized later this spring, and Rocket League will come to the Epic Games Store later this year.
"In the short term, nothing will change at all," Psyonix affirmed in a blog post. "We’re still committed to providing Rocket League with frequent updates that have new features, new content, and new ways to play the game for as long as you’ll have us."
However, Psyonix didn't address the biggest question Rocket League fans are likely to have: will the game still be available on Steam? According to a press release from Epic, the answer is yes and no.
"The PC version of Rocket League will come to the Epic Games store in late 2019," Epic said. "In the meantime, it will continue to be available for purchase on Steam; thereafter it will continue to be supported on Steam for all existing purchasers."
In other words, Rocket League will always be playable on Steam if it's already in your Steam library, and Psyonix says it will continue to support the Steam version with all new updates. However, once the game arrives on the Epic Games Store, it will no longer be available for purchase on Steam. So yes, Rocket League is leaving Steam as a result of this acquisition, but it won't be removed with a hacksaw.
Rocket League will be the first post-launch Epic Games Store exclusive, but it's the latest in a long line of Epic exclusives, including Metro Exodus, The Division 2, and The Outer Worlds. The company previously said it will eventually start buying fewer exclusives, but from the looks of things, eventually hasn't started yet.
Epic CEO Tim Sweeney said that most people don't see all the ways the Epic Games Store is helping the industry.