Effective Tuesday 12/1/09: http://www.finra.org/web/groups/industry/@ip/@reg/@notice/documents/notices/p119906.pdf
Yep, looks that way, for traders who do not keep up on such things, and keep open positions over time. Brokers love those margin call fees!
It's because of the leverage. Don't read any more into it. If you're trading 2x the inverse on the SDS, for example, then you should have 2x the margin you would have on the SPY. Completely logical.