Most scientists work for scientific institutions (universities, research companies) where their employer has a license for all to read those journals. Just like the old university libraries where you could find all these journals in print. To these people there is not much of a hindrance and the digital availability may make exchange of ideas actually easier than it was before.
They do however keep curious bystanders out - people who have an interest in science but are not working in the field. This are the same people that did not have easy access to the journals (unless they'd hop on their bike and cycle over to their local university's library - assuming there even was one nearby). For these people access hasn't worsened much, but definitely hasn't improved either.
All in all I can't really agree with them hindering the exchange of information, though they could very well make it a lot easier - for example by making everything older than say a year or a few years free to access, leaving the latest and greatest to those that are willing (and capable) to pay for it.
Somehow these journals need to be paid for their work. Peer review is not free, publishing is not free. Just putting it all out on the Internet for free is not a viable business model, as is proven by the many pay-to-publish crap journals discussed here many times recently.