They record High Definition format (HDV) to miniDV tape. I do not re-use the tape - the tape is the archive and tapes cost only about $3 each (8-packs at Fry's are $24.99 - tapes can be had cheaper in quantities at tapestockonline.com. Special HD tapes not required.
I presume you are referring to a high definition tapeless consumer camcorder environment. Um... yeah. A few options so you do not lose the high definition video... You can fill external hard drives, but many people do not consider hard drives real archive storage - back up, maybe, but not archive because even as good as they are, hard drives will fail. You can invest in a BluRay burner for your computer - I like the externals from LaCie. The BluRay discs are a bit pricey, but they do start with 25 gig blanks (and get larger. Using regular single layer (4.7 gig) or double layer (8.5 gig) DVD blanks may work, but they really don't hold very much in comparison.
You *could* invest in a firewire port for your computer (if it does not already have one) and get/connect a HDV deck - or an HDV camcorder and export the video from the computer to miniDV tape over the firewire connection (a regular 60 minute miniDV tape will hold 63 minutes of HDV - or the equivalent of ~44 gig of computer hard drive space that uncompressed high definition video uses)...
Your experience/investigation is one - of several - reasons why the consumer tapeless camcorder environment is still not ready for prime time.
I have a Sony HD camcorder. Obviously, with the HD format, the memory on the camcorder fills up quickly. What is the best way to save/backup the old files without losing the HD format so that they can be deleted from the camcorder to make space for more?