Things move on, in the olden days you bought a horse, when it grew old and slow, you killed / ate / put it out to pasture and moved on to a new one.
Take cars for example. You buy a car, you drive it, have fun with it, got to work in etc.etc.. but you might
want to make it go faster, sound better, be more comfortable, so you BUY mods for it.
Someday all content will be available like this. You pay for the standard package, if you want something more than normal people you pay for more.
you wouldnt see someone walking into a car delaership demanding a free upgrade to leather because another type of car came with leather as standard. in the same way you wouldnt accuse antivirus companies from charging for protecting your computer with software updates.
The costs involved are so small, and you are paying for smaller developers time and effort. Whats the difference between downloading a mod you really want and a tv show you really like if they provide the same amount of enjoyment over time?
tis the future, though the standard of the mods is another issue alltogether..