The explanation given for 'Starbucks and Starbucks', by an employee of one of the two stores, is as follows:
Once upon a time, there was a Starbucks on a corner in the West End of Vancouver, and it was very popular. However, for one reason or another, it had to close down temporarily, to do some renovations or something of the sort.
While it was closed down, an entrepreneur/profiteer decided to fill the west-end's (small) non-caffinated gap in the map, and opened up a Starbucks - across the intersection from the original.
When the first store opened up again, however, it was discovered that there was more than enough busines for both of them (this is Vancouver we're talking about), and so they've happily coexisted ever since.
Incidentally, if you're a fan of holography and semi-related miscellany, there's a neat hologram shop next to one of them. It has no relation to Starbucks and Starbucks though, except that that's how you find it.