Is it a barrier, yes. But it is not *equally* so. DMs traditionally know, understand, and are not flustered by the idea of having to lay out more cash than other players.
I worry about this, because it isn't really true of those new to the hobby. If you take someone who wants to get into roleplaying games, who finally got some friends to try it with him, and he's asking what game they should play, then D&D becomes a
terrible gateway into the hobby. Savage Worlds, Fate Core, and Dungeon World (as a few examples) are all really good games, and ones suitable to newbies. They're all contained in a single book, each of which would sell for about the same as a single D&D hardcover or less, with PDFs as options. Add onto this the fact that Savage Worlds has a 16 page free intro product, Fate Core is pay what you want for the PDF (free preview), and Dungeon World is Creative Commons with a webpage with enough rules to play the game also for free. So, someone new picking up D&D has to trust that the the game is worth buying 3 books for ~$90 total, sight unseen, over these products that can be trialed.
Add to that the fact that if the D&D books are the 320 pages some people are suggesting, you're asking someone to read at least 640 pages + monsters to play the game just to get started. That's daunting. A lot of roleplaying curious people aren't sure what its all about and are unsure about playing. Many of these people who I interact with online don't have a regular group nearby that they can try and get their feet wet with or are intimidated by the thought of joining an existing group or just want to play with their friends. I think there are a lot of people out there who want to try it out because they've read about it or heard about it online, but aren't really sure how to get started. For these people, a single product for $0-$25 with all rules in a self contained book is vastly superior to a 3 books set for ~$90.
I think a free intro product in PDF format would go a very long way to alleviating some of these concerns. However, there's still the problem that if they like the intro product, now they have a much higher investment to make for D&D than other RPGs which are just as good. I simply don't know how that can be justified.