Correct, volume isn't always everything. However, that is only the case when there are large differences in profit margin. In this case, there isn't much difference. The Z10 (which I've used a little bit, not every day) is an average device these days with some neat features. Nothing earth shattering. Its as average as an iPhone or any number of Android devices. The sales however, have been disappointing. The largest factor, is that without any large distinguishing feature, most people have already moved on from Blackberry to other smart devices.
However, as I said above, its all about the Q10 for Blackberry. It has a much higher profit margin, and they will sell a ton. There are plenty of people out there just waiting for their "real" keyboard. With very little competition in that market, and a loyal fanbase in that market, they should do well. In the first quarter. They will probably even pull a million or so iPhone/Android users back with the physical keyboard. However, when you consider that Apple is averaging about 30 million units a QUARTER over the last two years or so, that doesn't really make a dent in market share. The Q10 will get most of its sales from people that have waited 2-3 years for the next generation Blackberry, that didn't migrate away to touch platforms. Blackberry's own estimates are that they will sell multiple 10's of millions of Q10's. Apple does that every quarter. Quarter after quarter. They have such a huge installed base, most of their sales at this point are people aging off of their iPhone 3gs/iPhone4.