I've had my new 5 string washburn for over a year know, (i hate this bass with a passion) and have never changed the strings. nor do i have money to, i just wish one would break one day, so i could get a new set, or just throw the bass in my closet for a decade.
and i've changed my guitar strings once, when i got it, (there almost falling off know) but the thing is such a p.o.s. that its not worth it. (i also hate it with a passion)
ive changed the strings on my acoustic bass (my first bass which i will have had for 2 years on the 13th) only four times, three if you don't count the flat wounds that didn't fit.
never really needed a string change, even now the strings (phosphorus bronze) are dark and dingy, and it sounds better than when i first got it.