Okay, I could not find this in the specs, but I do find this fishy. When querying a Windows DNS server it will give out an authoritative answer (aa bit set), but without an AUTHORITY section.

dig +nocmd +noidentify +multiline @ns5.msft.net. soa hotmail.com

;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;hotmail.com.	IN SOA

;; ANSWER SECTION:
hotmail.com.	86400 IN SOA ns1.msft.net. msnhst.microsoft.com. (
		    2009100802 ; serial
		    1800       ; refresh (30 minutes)
		    900        ; retry (15 minutes)
		    2419200    ; expire (4 weeks)
		    3600       ; minimum (1 hour)
		    )

;; ADDITIONAL SECTION:
ns1.msft.net.	3600 IN	A 65.55.37.62

And it gets worse:

dig +nocmd +noidentify +multiline @ns5.msft.net. soa miek.nl   

;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 35647
; flags: qr aa rd; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;miek.nl.		IN SOA

;; AUTHORITY SECTION:
.			3600 IN	SOA ns1.msft.net. msnhst.microsoft.com. (
		    2009071743 ; serial
		    900        ; refresh (15 minutes)
		    600        ; retry (10 minutes)
		    86400      ; expire (1 day)
		    3600       ; minimum (1 hour)
		    )

;; ADDITIONAL SECTION:
ns1.msft.net.		3600 IN	A 65.55.37.62

WTF?? MS rules the internet and is authoritative for . ?