Sure, but there are exclusive VR games. (Half-Life Alyx isn't exclusive to Steam Index, I don't think any games are only for that headset/controlset, but Alyx does apparently have some minor Index-exclusive content.)
If a game idea came along that for instance used the multitouch touchscreen, something that couldn't really be done comfortably with a mouse, you could see that as being considered Deck-exclusive (albeit touchscreen laptops could probably play it just as easily.) If Valve came up with a touchscreen-optimized way of playing DOTA2, that might make sense as a separate app (though it'd probably made more sense as a mod for the main game, so as to not split the player base.) Or if there was an AR-type game or a game designed to take advantage of WiFi geo-locating, that probably would be primarily a Deck game (even though a laptop could enjoy it about as well.) I could see a scenario where Valve might have made a game "for Deck" that might be playable on a PC, but it really came into existence for Deck (similar to how Steam has stuff like Fallout Shelter and some Angry Birds games, and they work but they're made for something else...?)
I mean, we're living in a time where Valve is one of the biggest names in gaming yet has made 5 games in the past 10 years (and of those, we'd probably all struggle to name them because they're mostly updates of existing games rather than sequels or new titles,) so it's no surprise that there's nothing specifically made for Deck. They're barely making
any new games as it is. But they got inspired by VR (or were economically driven to bank off VR, depending on your viewpoint) to finally make a new Half-Life product, and that helped put Valve at the top of the VR market. You could maybe see them feeling equally jazzed/driven to make a calling-card touchscreen game or a great small-scale game to celebrate/push Deck, and if people played it in other ways, so be it, as long as it helped get Deck and Valve on the minds of the general populace.
Supposedly, actually, the project "Citadel" might be kind of one of these types of game, where it's not excluding PC, but it'll have that kind of "Best Played on Deck" feel to it.
Half-Life 3 is reportedly not in development, as ‘Valve focuses on Steam Deck’ It’s claimed that all attention is being placed on games that better fit Valve’s upcoming handheld Half-Life 3 is not in active development, and Valve is instead focusing on Steam Deck friendly titles, according to...
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