creative writing - Is it true that writers don't really need agents and they can just query publishers directly, as Dean Wesley Smith says?

While I tend to agree with the writer & publishing guru, Dean Wesley Smith, that agents are usually a liability and that it is wrong for writers to hand over their royalties to them, I am not sure about the part where he says they are totally unnecessary for submitting your work to publishers. Because it seems to me that that is the one thing that agents are actually useful for: acting as filters or slush-readers for the publishers.

According to him, writers can actually ignore the injunction on the big publishers' websites that says 'no unagented submissions' and simply submit their queries anyway, and they often do with good results. In other words, in spite of what they say on their websites, the big publishers actually DO read queries and take work from unknown writers directly.

I'd like to know if this is really true. Any insiders here that can confirm this? Dean has many years of insider experience in the publishing industry and seems to know what he's talking about. But I am still unsure as to just how true it is that editors in these big publishing houses actually read and respond to queries directly from writers in spite of what they say on their websites.