Apple has at last fully -enabled Web browser-based song previews of tracks offered for sale via iTunes.
Apple introduced iTunes Preview in November 2009. However, while you could review song listings using a browser, you were unable to listen to the songs without sparking up iTunes.
This has now changed. Apple is now offering browser-based song previews (30 seconds) using Quicktime to furnish tracks encoded at 44.1 AAC 300+ kbits/second. If you like a track you can then hit the button to purchase it through the Apple music service.
Try the new feature on the iTunes Charts page.