It looks like it's the end of the road for Microsoft's suite of Expression design tools, as Peter Bright over at Ars Technica notes.
Expression Design 4 is being phased out entirely, though it will be patched through 2015. Expression Web 4 also is being dropped. And Expression Blend - which made it up to Version 5 - is being folded into Visual Studio.
Microsoft first released the Expression tool family, targeted at designers rather than developers, with much fanfare back in the mid-2000s. Expression Web was codenamed Quartz, Expression Blend, Sparkle; and Expression Design was known as Acrylic. A preview build of Expression Blend 5 was bundled in with Visual Studio 2012. Microsoft has been touting Expression Blend as a useful tool for building Windows Store and Windows Phone apps.