I think Tupperware has become a generic name, like Hoover and Biro, Mikey, hence the Ebay/Amazon entries.
Things have moved on in the 30 years you've had yours and some of the copies are pretty good; clip-on lids are far easier to use than the old Tupperware system too.
I agree with bhg481 on this. The original Tupperware eventually went yellow and felt sticky and it was expensive. I buy containers in all shapes and sizes with the clip on lids, some from the Pound Shop. Keeps food just as fresh and can be used in the freezer. x
I have Tupperware that must be as old as yours mikey - also bought some at a car boot sale last year. Great quality and will last for another 30 years.