The ability to store attachments directly on the task is a new feature in Salesforce.com that was part of the Winter '11 release, if your administrator has not yet updated the task page layouts to include the attachments related list, then it may appear that the attachments were not uploaded.
New Task Creation Page
If you do not already see the 'Attachments' related list (highlighted in green) - follow the directions below to add the Attachments related list to the TASK page layout:
1. Your Name
2. Setup
Under App Setup choose:
3. Customize
4. Activities
5. Task Page Layout
6. Choose Edit next to the Layout (do the following - below- for each Task layout)
Editing the Task Page Layout
1. Choose Related Lists
2. Click on the Attachments related list
and
3. DRAG & Drop the Attachments related list in the related list area below Custom Links
4. Click SAVE