MS aren't promoting Silverlight for the PC so the assertion they don't want HTML5 makes little sense when they are gearing their tools around it.
Adobe has Flash but similarly seems set/resigned it is on the way out, they seem to be killing it faster than they need to if anything. HTML5 content tools are a massive money pit for Adobe.
Apple don't have a rich web alternative of their own. So unless you think they simply want everything done as a native app rather than a website, which seems a little like a conspiracy theory, that doesn't work either.
More likely, MS and Apple are simply tremendously conservative because they have to support their browsers for several years, unlike Chrome and Firefox who just release a new version and change their minds on feature-sets without the need to provide enterprise support.