I checked the code extensively and there is no limit to number of items you can display although you need to be careful when adding new items so as to get the layout right. Are you sure you have more than 10 Portfolio items created? I would create a few extra items and see if the portfolio items appear there.
One thing to keep in mind – if you use the arguments – portfolio_link=”http://portfoliotheme.org/wired/filterable-portfolio” link_text=”Our Work” in the shortcode, one of the portfolio items will be used to mask the link to the portfolio page. If you remove the same two arguments from the [show_portfolio] shortcode, all the items will appear. This is required so that we can get the isotope layout right when the screen size shrinks.