If this was a console game, where I could really only store my games there, then you'd have a point. My problem is that "you can just get more space" is a fallacy. Let's do some simple mathematics, and allow me to show you why the point is crap.
Let's start out with a 500 GB storage drive. Of that 500GB, about 20 is the OS, another 20 is the non-game programs, and there is a mathematical error of about 20 GB. That means you theoretically have 440 GB of storage for your media. Let's say that the storage medium double is size every 36 months, because you either get a new computer or install another HDD. Let's also say that the media being stored quadruples in size every 48 months, representing the shift from DVD to Blu-ray and such like.
Now, you'll start off with a certain amount of media. Let's peg this at a dozen CDs, about 20 DVDs, 10 games at 10 GB each, and about 10GB of other data. The rate of acquisition for new media is a CD every two months, a DVD per month, a game every month, and the other data increases at a rate of 5 GB per month. In the first year you go from 198 GB to 484 GB. By year two you're at 770 GB. By year 4 (when Blu-ray is introduced at 25 GB), you're at 1359 GB. Where media completely outpaces the storage is 64 months in, where you get 2005 GB of media, with only a 2 TB platter available to you. By month 72 you're at 2328 GB of data, and only have a 2TB drive to work with.
Now, imagine that average 10GB of games has been bumped up to 30 GB. Perhaps even 40 GB. What then? The amount of storage space needed is huge. Now add in the need for redundancy, because things break, and the 3 TB of data actually requires 6 TB. That is, unless you've got a substantial cash flow and can actually make a RAID array.
I for one built a RAID 5 array of 2 TB drives back when they were cheaper, but they are only now actually returning to the price of 3+ years ago. Not sure about you, but I put a huge dent in that "6" TB of storage, without even considering the Steam based games storage.
I'm not sure about you, but I can't see having anything less than a 2TB storage drive on any computer. Budget gamers skimp on the storage, in order to buy a better GPU and CPU, thus making a 1 TB drive a common factor. I'm not sure how you'd fit Steam, let alone any other media, on only 1 TB. Start making games much bigger, and that 1 TB is massively inadequate.