Apple’s share of total app downloads fell by 24 percentage points between 2008 and 2010, from 81 per cent to 57 per cent, as the number of app stores tripled from 18 to 57, according to the latest study from research2guidance.

But in the first quarter of 2011, Apple halted the decline, increasing its percentage share by two points to 59 per cent, thanks to the actions of iPad owners, who are heavy app users. The analyst believes that the iPad support will hold up, as long as the other app store operators fail to come up with a competitive app store offering which addresses the tablet users, and non-iOS based tablet shipment numbers remain low.

Research2guidance concludes that if Apple manages to slow down its market share loss over the next two years, it will be difficult for other players to overtake Apple for a long time. Even though Apple’s competitors might be able to push Apple’s market share down to less than 40 per cent by 2015 (assuming the same market share drop as within the last two years), Apple will still keep the heavy downloaders from the early days for a long time.

The analyst says there are two factors that are narrowing down the time for competitors to catch up. The first is the mass-market effect: smartphone penetration will reach 50 per cent in most developed countries by 2014/2015. The more smartphones become a mass-market phenomena, research2guidance says, the less app downloads a new user will add. The second factor is the lock-in effect of downloaded apps: the more apps are downloaded and the more money is spent on apps, the less likely the user is to switch to another platform.

The findings come from research2guidance’s latest report, The Smartphone App Monitor Vol. 2. You can read a blog post about the findings from report author Ralf-Gordon Jahns here.