Here is an offical explanation for the revision:
(I corrected the grammar flaw)
"...the criteria for Asperger syndrome in the DSM-IV are (is) flawed and hard to implement in practice, as highlighted by a number of researchers10,11,12. At least two problems exist: It is often difficult to establish whether single words were spoken before age 2 and phrases by age 3, as required for the Asperger diagnosis. Individuals receiving this diagnosis typically come into the clinic in middle childhood or later, and parental memory may be understandably vague. For the increasing number of people diagnosed in adulthood, the issue is even more problematic.
The other major problem with applying the current DSM Asperger criteria comes from the precedence rule: diagnose Asperger disorder only if the individual doesn’t meet criteria for autistic disorder.
The Asperger diagnosis is distinguished from autism by a lack of language and cognitive delay. However, language and cognitive delay are not diagnostic criteria for autism. So, to fail to meet criteria for autism, a person with Asperger syndrome must not show the communication impairments specified for autism. Since these include “marked impairment in the ability to initiate or sustain a conversation,” most — if not all — people with Asperger syndrome do meet diagnostic criteria for autism."
Really? It's that hard for a parent to know if their kid spoke at an appropiate age? One would think a parent would remember that, since it's pretty deviant if the child doesn't.