Does the 255 limit for number of columns in Desktop apply to Report Services Documents in Web?
No. This limit is not the same in Developer and in Web in Strategy version. If you create a grid with over 255 metrics or attributes, this can be used as a dataset in a Report Services Document. While the exact limit for the number of objects which can be pulled in by a single dataset in Web is not hard coded, it does respect the governing limits put forth for the Intelligence Server(s) utilized:
When executing Report Services Documents in Web, users must additionally be aware of the limits for XML Generation as well as Exporting governing settings:
