This is no different than many other platforms out there. How does a developer get their game to run on the PS2, PS3, Xbox, Wii? Do you think they can just press the DVDs and send out the boxes?
No, they need to pay the manufacturer of the box for the license key, otherwise the DVD is nothing but a shiny bit of plastic when inserted into the game boxes.
Apple can do this because it's a new platform. Any developer wants in on the potential income of the platform, they have to share.
Don't forget that Apple pays for the cost of the Store and the distribution.
If you're a developer and your application's size is roughly 50 MB, do you know how much it would cost you in bandwidth alone to deliver it to 100,000 clients? In the case of an iPhone/iPod Touch case, Apple foots the bill. If you have a free application to deliver, Apple foots the whole bill with nothing coming in.
Second, if you're a developer that wants to sell directly to the customer, that means you have to have your own system to handle credit cards. Do you have any idea how much the credit card companies take? I have such a business and I pay the credit card companies $0.30 + 3% of every transaction. If I were to sell a progam for $3 that means the credit card companies' cut is $0.39. That's 13% of my income going to the credit card companies (and that's not counting charge backs and other fees like $395 per month system access fee). Apple saves you that expense.
So it's not all greed.
Everything has pros and cons. With the App Store, the pros are numerous. Better security, better and simpler delivery, more exposure etc...
There are two cons that I can think of:
1) Income sharing. Though not as bad as you think it is because it save the developer the expense of distribution and credit card handling and stuff like that.
2) Loss of control. If Apple doesn't allow your application for whatever reason, then you don't get to sell it. To me, that is the biggest disadvantage.
I don't think Apple is developing an alternative to Photoshop, but stranger things have happened before.
That being said, Adobe can't and shouldn't be trusted. They're a business, and the first responsibility of any business is to maximize profits for its owners/shareholders. Logically, to maximize profits, a company should minimize its expenditures. To minimize expenditures and cost, logically, Adobe should try to focus their development efforts on as few platforms as possible. Since Windows is the bigger market (by a huge margin), logically, Adobe should restrict their development resources on Windows. Logically, if they could manage to move all their clients to that single platform, then they should do that.
In the late 90s, Adobe was in the process of doing just that. They started releasing windows versions of their software ahead of their Mac versions and in the case of Acrobat, releasing inferior versions of their software, and in the case of Premier, stopped development for the Mac altogether.
Their aim was to gradually make the Macintosh platform as unattractive as possible to their clients in order to encourage them to move to Windows. Adobe even put a notice on their own website, recommending Windows to their Premier customers.
To be sidelined by one of the biggest software developers for the platform sucks for us as Mac users and is very dangerous to Apple as the owner/developer of the Mac platform.
It was highly publicized that Adobe bluntly refused to keep development of Premier for the Mac going and move it to the then upcoming Mac OS X. Apple said that because of that, they went looking for a video editing package for the Mac and bought what was to become FinalCut from Macromedia.
Apple managed to punish Adobe severely for their attempt at neutralizing the Mac platform by nearly taking away the whole video editing market from Adobe. I believe that it was a hard lesson to learn for Adobe. The lesson was not to try to force Apple into a market, otherwise Apple would take it away from them easily. I believe one of the main reasons behind Adobe's purchase of Micromedia was to take it before Apple had any reasons and chance to buy it for themselves.
Maybe Apple had some info about Adobe's intentions regarding their publishing suite and built Aperture as another club to beat Adobe with into submission. While Photoshop is a formidable and very sophisticated piece of software, I have no doubt that Apple could build something that fills the void left if Adobe decides to take it Windows-only; and I believe that Adobe believes the same thing after what happened with Premier and FinalCut.
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Is Apple Building A Photoshop Replacement?