This of course, to increase bike turnover and prevent people from hoarding bikes. The consumer's ability to reliably have a good expectation that a bike will be available when and where they need it is critical to success of the system.
Melbourne's bike share is great for tourists. As a tourist, one often places oneself in neighbourhoods where the walk is very long, but taking a cab seems wastefully short. Additionally, taxis are a little sterile and boring, as they do not easily allow for the ability to randomly stop, change directions, or do something impulsive, which is one of the most fun components of the tourist experience. Cycling is the best compromise between the two.
The Melbourne bike, in my experience, was extremely tourist-oriented. According to its Wikipedia page, it is underperforming ridership expectations. (This is not surprising; estimates for public transit usage are consistently too high so it's not surprising that bike share would be the same.) The vast majority of people I saw using the bike share had obvious tourist tells. While Melburnians do ride bicycles a lot, most of them tend to own their own bikes.
In Mexico City though, the Ecobici system seems to be well-utilized by locals. One reason certainly must be the price discrimination at work:
That is an insane price gap: the first 7 days cost 300 pesos ($19.50 US), and the next 358 days cost another 100 pesos ($6.50 US).
The Melbourne prices offer a big discount for the yearly subscription as well, but they are far more tourist-friendly:
Considering that $8 Australian is the equivalent of 95 Mexican pesos and that Australia's per capita income is over 2.6 times that of Mexico, renting a bike for a week in Melbourne is more than 8 times cheaper than renting it in Mexico City. Of course, another way of putting it is that Mexico City's yearly price is more friendly to locals (58 AUD = 686 MXN).
Mexico's lower relative wealth would also make renting bikes more attractive than buying. Buying a bike can be expensive, so investing capital up front on a bike makes more sense for a Melburnian than it does a Chilango. I would also suspect that people feel less likely that an unattended bike will be damaged or stolen in Melbourne than they do in Mexico City, making ownership more attractive down under. So it's no surprise that I notice that less than 30% of those using the bikeshare in Melbourne were locals, more than 90% of those using it in DF live here. (Note that these estimates are pretty arbitrary since they rely on my subjective snap assessment of who is, and is not, a tourist.)
There are other factors beyond price that will affect utilization. Melbourne has only 51 stations while Mexico City has 444. True, Mexico City is a larger and much more populous city, but check out this comparison of station density (both screenshots are approximately, but not exactly, 11 km^2):
It makes sense that residents of Mexico City use the bike system a lot more than those of Melbourne. They're more easily able to commute, run errands, and so forth with confidence that there is a station near their destination. When catering to tourists, a higher density and distribution of stations is not nearly as critical; you simply need to prop them up where all of the tourist attractions and hotels are.
Melbourne's system is more tourist-oriented than local-oriented in another way, not nearly as obvious: a lower barrier to registration. In Melbourne, you simply insert your card and authorize it at the machine. In Mexico City, most of the stations are only for pickup and dropoff. To actually purchase a subscription, you must go to a "fourth-generation" machine, which are far less common (they are marked with triangles in the above pictures). Once at one of these machines, you have to enter full name, phone number, e-mail (twice), and date of birth on a touchscreen. Not only that, there are serious issues accepting non-Mexican cards. I've been trying for days, and I still haven't actually been able to take one of the bikes! Frustrating!
I haven't read a lot of reliable data on the ROI of civic and regional governments spending money to promote tourism, but from a libertarian perspective I'm always going to be skeptical about any project that takes money from the residents in an attempt to increase tourist dollars. Bike shares in heavily congested cities like Mexico City, or perhaps those in China, make more sense to me than they do in cities that are simply "pretty", like Melbourne and Vancouver. In non-congested tourist cities, it seems like the private sector should be able to handle the tourist bike rental market just fine.
Despite my libertarian bias, having a convenient city-wide bike share program is great for frequent tourists like myself. With a sufficient density of well-stocked bike stations, a bike share provides nearly as much autonomy as your own car while getting exercise and seeing the sites. Riding a bike to the grocery store or even the museums and tourist attractions make you feel more like a local.
Now, if only the one here would take my credit card.