I think one valid reason to need a typeface which might look similar to something else is that of the foundry's EULA. This is the problem I'm facing at the moment.
I LOVE Whitney, I licensed the entire package, and have used it in different projects, but suddenly find that I cannot use it because of the potentially cost-prohibitive need for extended licensing. I want to cry because I cannot afford it.
I've replaced it with Myriad, for now, because I do have that and it didn't create too much of a switch-a-roo hassle. But, it isn't as interesting. Boohoo.
Anyway, if anyone has suggestions for a super-family--condensed, compressed, regular plus all the weights--which also has a EULA that allows for embedding in PDF and Flash (presentations) which can be posted on the web I'd be curious to see it.