On one hand, some people might say they paid a huge amount of money for a product that had this (locked) functionality built in, and they have the right to hack it. On another, it's not a trivial amount of effort to write the software that does the analysis, so I could see why a company wants to protect its intellectual property. Otherwise, why would they bother? They would have to ship the device at a higher price to cover the cost of developing the features.
I think the solution here is for the companies to implement reasonable security. Cisco is famous (at least lately) for shipping crippled hardware that is fully capable of performing the functions that are unlocked by various licenses. They implement it as a soft key that ties in with the device serial number (i.e. pay your money, go online to Cisco, give them the license code and your serial number, and they give back another code to enter into the device. And presto, instant feature. Another example I have right here at work is an IBM DS3500 disk array. There are feature keys for everything -- volume snapshots, remote copy, SSD support, increased number of hosts, and a very mysterious, strangely named "Turbo Performance" option [1]. So this is nothing new -- my disk array is running the base configuration and I'm fully aware the controllers in it are shipped with these capabilities. It's weird having to buy $10K pieces of paper, but I see why they do it.
It seems like Tektronix was relying on security through obscurity and they assumed no one would try to build hardware keys to work around their feature protection. HP recently did something similar with the ProLiant and Integrity server line that Oracle/Sun did a while back -- they simply stated that no firmware upgrades would be available on their machines without a warranty or service contract. As someone why buys old hardware for fun, it makes it difficult to get it to the last firmware that HP released for it. But, fixing firmware isn't free, so there's that angle as well. I think the HP/Sun/Oracle stuff is aimed more at forcing you to buy service from them, so it's a little different.
[1] Side note - even the reseller who sold us the device couldn't tell us what Turbo Performance did. After a lot of digging, I figured out that this option is used when you add tons of disk shelves to the array, and it lifts an artificial performance cap on the controllers.