You can create email accounts for any legitimate email address. (The creation will fail if it's not legal syntax, like
me@@myemai.com) or if, when questioning the server for its requirements there's no server there (myemail.com doesn't exist), the account doesn't exist (me,ail.com exists, but there's no account named "me" there), or the email server rejects the request (you can only connect to it from certain IP addresses, MAC addresses, etc.)
As far as a widget for each account, no.
(The last paragraph is the tl;dr version)
As far as push, that depends on the server. RIM queried the servers and pushed anything they got. GMail pushes, but they don't query foreign (IOW, not Google) servers for you, the server has to be set up to push to Google's push port.
There are standards, and when an SMTP server says 220 it better mean the same thing it means to all other SMTP servers, or whoever wrote that one isn't going to last in the business very long. But push? There's no requirement that an email server does push. (IMO, there should be, but it would probably cost in the billions to implement it on every server in the world that doesn't do it yet.) That's why, in an Android phone you can set a polling interval (called the sync time), so the phone pulls from the server every X minutes (whatever you set).
Some people need to see every email as soon as possible, and the heck with the battery drain. Some people need a long time between charges and getting new email every hour is good enough.
RIM's philosophy was like Apple's: "We know what you need and that's what you get". (Even if this year they said "you don't need X" and next year they're touting X as the next greatest thing.
Android's philosophy has been "do it any way you like it. We may not put your app in our store, but we don't care if you write it and half the Android users in the world use it." But that means that you do have tomake choices, and developers do have to develop apps.
We have a developer's section, and some of the developers read it just to get ideas of what to write. You want an email widget that can be attached to only a specific account? And you can put more than one on the desktop at a time, one for each account? Post there, and maybe someone will take up the challenge and write a widget to do it.
