From what I've seen over the years, there's 2 kinds of NAS:
-inexpensive ones, usually with abysmal performance (and often various other issues, limited protocol support, a sucky management interface, limited capabilities, etc)
-OK ones, at ridiculous prices, which is
especially apparent if they have more than one HD
If they made good/fast and cheap NAS devices, everyone would have one (I'd probably have a dozen). Before you buy one that you can actually afford, check the reviews, you'll likely see it has really bad transfer rates. Why? Because they go for underpowered embedded processors and such to keep their costs down so they can sell for cheaper. As you found out, most also use a ext filesystem or such, also to keep their costs down as jaclaz mentioned.
LaCie products mostly fit in description #2:
-$319 for a 1GB
LaCie Ethernet Big Disk (single drive), considering a good 1TB HD can be had for
under $140 so ~$179 for the drive-less NAS with no expansion capabilities whatsoever ($179 overhead on every drive, more than double the cost of he storage space itself)
or if you want something closer to what I'd call a "real" NAS i.e. something with more than 1 drive, with some room for expansion, and a good capacity:
-between $850 and $2020 for a
LaCie Ethernet Disk RAID with between 1TB and 4TB capacity. You can buy 4TB of space (4x 1TB HDs) for $560 and then throw that in a brand spanking new low power PC (built around an Intel Atom processor or VIA board or whatever you want) for MUCH less $$$ (4TB for less than LaCie wants for their 1TB model). That will also run any OS you want, use any filesystem you can think of, use any level of RAID you might want, and do anything else you want (any protocol, app, or whatever you want it to do). There's even some great specialized software made just for this task e.g. OpenFiler or FreeNAS.
Anyways, a popular option is also the Linksys NSLU2 at around $85, but again, it's single drive (and no gigabit ethernet). Throw one large HD in that, and it'll be sufficient for some mp3's and photos. But if you want more than that (like your video collection and such), you're better off not buying a NAS, at least when it comes down to price.
As for the ext drivers, they work well, but there's been a glitch with them for months unfortunately, so the bug fixing speed isn't stellar... (just try mounting a TrueCrypt disk image, your PC will BSOD).