For example:

* Order History – included in order management
* Email Notifications – included
* RSS Feeds for Categories – all YAK products are categorised, so you get this for free through WP anyway
* Fast Product Search – again comes for free in WP
* Shipping Rate Calculations – YAK can calculate flat rate, or by quantity or by weight
* Shipping Discounts – included in promotion functionality
* Promo Codes & Coupon Codes – as above
* Utilises WordPress pages, or posts, to create products – as YAK has, since the beginning
* Products can have multiple options – included
* Upload downloadable products – YAK supports downloadable products, although this is perhaps not as user-friendly a feature
* Download sales data – you can export order (sales) data from the order management screen
* Configurable Out of Stock message – included
* Basic Stock Control – included
* Various discount options – see promos above
* Several payment options – YAK supports PayPal Std, PayPal Pro, Authorize.net, basic page (cheque, deposit info for example), Accounts Receivable, and manual credit card processing.

I think the featuresets are comparable, frankly.