if you look at diagnostic criteria for both autistic disorder and aspergers disorder, they are THE EXACT SAME when it comes to this part.
"Restricted repetitive and stereotyped patterns of behavior, interests, and activities, as manifested by at least one of the following:
1. encompassing preoccupation with one or more stereotyped and restricted patterns of interest that is abnormal either in intensity or focus
2. apparently inflexible adherence to specific, nonfunctional routines or rituals
3. stereotyped and repetitive motor manners (e.g., hand or finger flapping or twisting, or complex whole-body movements)
4. persistent preoccupation with parts of objects"
so no, you dont have to have "special interests" to be as or ad, altho its really common in as. diagnostically, you only have to have one of those 4 requirements to fit the criteria.
my son does not yet have real special interests like most talk about, where they know every single little bit of information on a topic, but he does have restricted interests when it comes to video games or tv shows. that may or may not change as he grows older and able to read and research, we'll see. his dad is similar, but he does tend to obsess about certain topics or video games for a period of time.