Sorry, I don't see that problem here. When I set my page size to 11 wide by 8.5 long, it exports as a landscape document in PDF. I did find the following note at http://sqljunkies.com/WebLog/ktegels/articles/1526.aspx, which may help explain the issue you're seeing:

"When attempting to export a report in landscape format to Adobe Acrobat Printer your default printer must support landscape mode.

"While researching the capabilities of SQL Reporting Services my default printer was set to "Microsoft Office Document Image Writer" which only supports portrait. Every time I extracted to Adobe, my reports were saved as portrait. After I changed the default printer to a driver that supported landscape mode I was able to extract the report to Adobe in landscape mode."

Check to make sure your default printer supports landscape mode.