Yes, however, the desired "lock-in" is to the tool, which sells, not the Flashplayer. People are used to developing with Flash Professional and have AS3 codebases, etc. If Adobe successfully targets HTML5 instead of Flashplayer, these people can (and in all likelihood will choose to) continue to use FlashWhatever Professional and even their AS3 codebases.
The player is merely a medium, though by authoring it, Adobe can advance the state of the art more quickly than the browser makers can agree on anything. This does make Flash Professional a more compelling environment.
But let's pretend for a moment that 95% of browsers got feature-coherent on the level of Flash. Why would Adobe care if the player were "all browsers", instead of Flashplayer?
Would they care because if they were targeting all browsers, they'd be effectively targeting a level playing field in terms of the base technology? Would it end up like Dreamweaver, which also targets a common base technology?
I'm going to argue "not necessarily, and in this case, no". And the reason is that anyone today can target Flashplayer. The playing field is already effectively level on Flash. Tons of software outputs SWFs. There are even Flash Professional wannabes, but they're not as good as GIMP is compared to Photoshop, and we know where that thread leads.
Speaking of that, consider Photoshop. It is hugely popular in spite of the fact there is zero infrastructure lock-in. Literally bazillions of programs can view and edit Photoshop-produced files. It's thriving while Dreamweaver, relatively, stagnates.
Dreamweaver's lack of dominance, IMO, is likely related to other factors. (I'm not sure why, but I don't know any professional web developers that use it.)
Iff Adobe could get Flash-quality and quantity on 95% of browsers using HTML/CSS/JS, I'll still bet you a pint they stop work on the player. Chrome 14 just added audio synthesis, so we're getting there!
Adobe's not going to stop working on the Flash Professional-style tools, though, even if it is outputting HTML. People buy Flash Professional for the features it provides both to the designer and for the end result. No one actually cares if there is a plugin in the middle or not.