Sony has introduced its second-generation Reader Digital Book, which will go on sale for $300 later this month at Borders stores and from Sony’s website. It supports eBooks, PDFs and Word files, and even MP3s.

The PRS-505 will be available in silver and dark blue, can hold up to 160 typical e-books, and has expansion slots for additional Memory Stick Duo or SD memory cards.

Unfortunately, it doesn’t have podcast or Mac support.

The lack of Mac and podcast support might seem inconsequential to Sony – but it means that the new media community can’t treat the Reader as another platform. Nobody’s going to create daily PDFs, delivered as podcasts, to help make the Reader a useful platform. You’re basically limited to Sony’s selection of 20,000 downloadable ebooks.

As a result, the Reader is a still a niche product, despite the fact that it’s a good piece of hardware that’s been heavily hyped.

If Sony were to offer Mac and Windows podcast clients for the Reader, and eBook plugins for Movable Type and WordPress, it could turn the device from a boring, closed system to a new platform for digital publishing.