Rainy weather definitely spiked demand in a big way (I sometimes wonder if Flywheel would have managed to make it over a few more hurdles if California had not been in an intense multi-year drought when I worked there). There was virtually no demand from Christmas to New Years, and then New Years Eve saw demand that was 10x what it was on other days. There are other extremely high-demand holidays such as Halloween and St Patrick's Day. Basically any drinking holiday, for obvious reasons, except 4th of July.
Uber is in many more markets, of course, though I suspect that a smaller number than you'd think are by far the heavyweights in their revenue and an even smaller number are the heavyweights in terms of improving their bottom line. They have surge pricing, which we didn't, and which is presumably better at turning demand into revenue than we were. Other markets may have different relationships with their weather than San Francisco did.
I would expect local competitors to exhibit far greater seasonality than any major multinational.
http://www.nyc.gov/html/tlc/downloads/pdf/2014_taxicab_fact_...
It looks like Taxis are seasonal and so they'll see a drop in revenue over summer (page 4). Though elsewhere they note that airport fares are up over summer.
It also looks like there's a large, several day, drop over the Xmas period every year, which could potentially make Q1 better than Q4. Although I know in the UK at least Xmas rates are higher.
Still, without seeing the actual figures and just eyeballing it, it's hard to say.
As you say though, they could have decreased costs just by dropping what they pay their drivers. Ahem, I mean the rate they offer jobs to self-employed definitely-not-employed independent contractors.
(I wasn't able to read the source article, so don't know if they've addressed that).