permision problems with /dev/usb/lp0

I have Debian Etch installed (Linux version 2.6.18-5-k7 (Debian 2.6.18.dfsg.1-13) (dannf@debian.org) (gcc version 4.1.2 20061115 (prerelease) (Debian 4.1.1-21)) #1 SMP Fri Jun 1 01:26:37 UTC 2007)

When I try to print with my epson stylus c64, nothing comes out of it.

I have all the packages related with cups installed

ii apcupsd 3.12.4-2 APC UPS Power Management
ii cupsys 1.2.7-4 Common UNIX Printing System(tm) - server
ii cupsys-bsd 1.2.7-4 Common UNIX Printing System(tm) - BSD commands
ii cupsys-client 1.2.7-4 Common UNIX Printing System(tm) - client programs (SysV)
ii cupsys-common 1.2.7-4 Common UNIX Printing System(tm) - common files
ii cupsys-driver-gutenprint 5.0.0-3 printer drivers for CUPS
ii gnome-cups-manager 0.31-3 CUPS printer admin tool for GNOME
ii libcupsimage2 1.2.7-4 Common UNIX Printing System(tm) - image libs
ii libcupsys2 1.2.7-4 Common UNIX Printing System(tm) - libs
ii libcupsys2-dev 1.2.7-4 Common UNIX Printing System(tm) - development files
ii libgnomecups1.0-1 0.2.2-5 GNOME library for CUPS interaction
ii libgnomecupsui1.0-1c2a 0.31-3 UI extensions to libgnomecups

Before power up the directory containing lp0 doesn't exist, after conecting /dev/usb/lp0 appears;

After power up the ls -ls output is:

0 crw-rw---- 1 root lp 180, 0 2007-12-27 21:00 /dev/usb/lp0

if you make (as root)
chmod 777 /dev/usb/lp0
Then the printer starts working.

¿ Why ?
Thank you