esto es lo que dice un articulo de msdn.
Cita: As described in detail in Understanding and Solving Internet Explorer Leak Patterns, the JScript garbage collector in previous versions of Internet Explorer manages the lifetime of JScript objects but not of DOM objects. As a result, the JScript garbage collector cannot break circular references between DOM objects and JScript objects, and memory leaks occur. In Microsoft Internet Explorer 6, these circular references are broken when the Internet Explorer process terminates. In Internet Explorer 7, these circular references are broken when users navigate away from the page that contains the leaks.
In Internet Explorer 8, the JScript garbage collector treats DOM objects referenced by JScript objects as JScript objects. Rather than wait until page navigation as in Internet Explorer 7 or process termination as in Internet Explorer 6, the garbage collector manages the lifetime of these DOM objects and breaks circular references whenever possible throughout the lifetime of the site.
Although Web developers should be aware of memory leaks created by use of programming patterns such as JScript closures in Internet Explorer 7 and earlier, those patterns no longer result in leaks in Internet Explorer 8.
http://msdn.microsoft.com/en-us/libr...42(VS.85).aspx
yo opino hay que tomarselo con cautela porque no me extrañaria que fuera motivo de pura publicidad.
nota: con esto no quiero decir que si podemos confiar en el uso de los closures, uselo con moderacion.