Skype works fine on IOS, Mac, Windows(obv), and Android as well.
The number of people who run linux on their desktop is probably on the same order as those who run BlackBerry - neither one of which has enough market presence to make it worth writing/maintaining apps for them. I'm pretty sure Skype isn't available from MS on OpenBSD either. (And, honestly, pretty soon, I wouldn't be shocked if Windows Phone doesn't get the same care and attention that IOS does).
The number of people who run linux on their desktop is probably on the same order as those who run BlackBerry - neither one of which has enough market presence to make it worth writing/maintaining apps for them. I'm pretty sure Skype isn't available from MS on OpenBSD either. (And, honestly, pretty soon, I wouldn't be shocked if Windows Phone doesn't get the same care and attention that IOS does).