Have this fairly often on quiet 737 domestics when the front 5 rows or so are blocked, though as earlier posted, if you have previously selected a seat in that area, not thrown out of it.(well I havn't been)
We were also the only couple in the front of an A321 in row 7, the entire rest of the front cabin was empty.... slightly strange!
This was 5 or six years back tho' where as on the 737 it has happened on a GLA flight very recently... there was a GCH in row 1 and me in row 3 then nobody else until row 6....