James' initial code is fine.
Woo uses an action hook in the content-single-product.php file, which you can find in this path:
You'll notice around line 61 the section dealing with after single product summary, to which woocommerce_output_related_products is hooked.
Removing that hook is the correct (and easy) way to get rid of those related products.
For those who had issues with the code. Dont edit that template file directly. the code below should go in your own functions.php file. Some times when you copy from the web and place into your code, depending on which editor you use, it can reformat quotes.
make sure the code is exactly as it's shown here, and dont forget the trailing semi-colon.
/* Disable Related products on single product pages */
remove_action( 'woocommerce_after_single_product_summary', 'woocommerce_output_related_products',20);