Coming from a Network Engineering background, but also being a VZW customer I can see both sides, I work with CenturyLink who thanks to a lot of all the heavy network traffic has provided us with a lot of contracts running more Fiber out to towers. Verizon is actually one of our biggest clients. (and it reflects that attitude with our discounts we get from VZW, vs sprint or AT&T)
It mostly boils down to one thing, Line Capacity.... That's the reason they want you to pay more, and if everyone who rooted their phone and uses free tethering bought the packages instead, Verizon would likely be increasing their towers line capacity a lot more...BTW I also use FoxFi and don't pay for it, so don't let it seem like i'm talking down to you guys, i'm only trying to explain it from their perspective.
Let us assume that customer A's device (phone) typically pulls say 3Mb/s...mostly burstable by watching a youtube video, or pulling facebook up and that the tower he's on is in a rural location, so an IMA Group of 8-16 aggregated T1's so the line capacity is 12-24MB/s MAX.
Then there is Customer B who rooted his device and uses his Laptop to download torrents, plays games, whatever, point is it's a data intensive service. it's no longer burstable, you have a continuous pull of whatever the device is running in the background, and your laptop. in a worst case scenario where that device is using the full, let us assume 8 Mb/s or 1 MB/s constantly (what mine is downloading at while waiting for Diablo III to install *Sigh*) that is quite a drain on that tower's line capacity. 37.5-75% utilization of that rural tower's Capacity.
Now how often is this true? Never in my experience, I've never seen an IMA Group hooked up to a tower, those are typically reserved for rural DSLAM's for DSL Customers, It's usually an OC Line or group of OC lines typically OC-12/24/48 (601/1244/2488Mbps Respectively) or what we've been doing as of late moving from ATM (OC Lines) to Ethernet (GigE or 10 GigE)
Anyway just wanted to let you guy's know Verizon's thought process from a business perspective....personally though? I won't be buying that package...Why?
This is the exact same thing that happened with MPAA when the VCR came out, the Same thing with RIAA when the MP3 Player came out, and also even more recently and relevant;
The EXACT same thing ISP's tried to do when Wireless Routers came out, I remember my parents receiving a letter when we were with Sprint DSL or Comcast back around the late 90's? Saying not to install one in your home and it was a violation of your TOS/Contract and they had ways of finding out if you did...yes that happened, and yes they wanted you to buy an individual Line/Modem Per PC....this whole thing will go the same way as that ridiculous notion did...Just give it time.