What's so bad about 60s, URLs, IBMs?
I think if you start using the apostrophe/plural convention, it really dilutes the distinction between plurals and possessives.
Then you get sentences like,
All the URL's in the world could not come up to this URL's length.
or
The 60's' main attraction for me was the music.
or
All the would-be cisco's in the world could not add up to cisco's stock price.
Ugh,
Joanna