For commerce entities, like products, bundles and variants - the output cache is not invalidated when you change prices or inventory amounts. It's probably because it doesn't require republishing the content to have it pop up in the view. All is well for smaller low traffic sites, but if your site is that small you're probably not using Episerver Commerce to sell your two products. On larger commerce sites, output caching could as well be key to achieve the performance needed, but it's quite risky if prices changing isn't going to clear out the cache of every product it touches.
Also, it should fire publish/save events so that your own custom stuff (lets say, Find-indexing) is updated with the correct prices instantly.
Especially in campaigns etc - products affected will not have their views refreshed immediatly (and potentially never if people keep visiting them).
Since commerce pages can be quite complex (displaying several products on one page, several prices, inventory statuses, article type content, images/assets, "Similar stuff"-searches etc), proper refreshing of the output cache for products should be fixed. Should also refresh the cache for all linked pages in Relations, softlink table and everywhere else.