It appears that Ubuntu devs/Canonical are following through on their promise to remove Wubi support (such that it was). They said they'd do this for release 13.04 and finally for release 15.04 there doesn't appear to be a Wubi.exe. It's not on the release website: http://releases.ubuntu.com/vivid/
Fine, no one can blame them for shelving the unpopular product - never mind that most of the problems with Wubi weren't difficult: they were simply bugs that no one cared about fixing. Well, that's not the whole story. In many cases the bugs were fixed, but the Ubuntu installer team didn't care to promote them (they had full control over Wubi).
Think about that for a second... a 5 line patch (average size) that would take all of 5 minutes to review and promote... but in some cases it took over a year to address. I know, because I patched a few myself.
So here we had a buggy product, getting flack from all sides. But the irony is that it was targeted and readily available to the most vulnerable of Ubuntu users - absolute beginners - who had no warning that it wasn't 'recommended': It is the first thing that pops up when you insert an Ubuntu DVD in Windows.
Ironically, even though Wubi was to be 'no longer supported' since 13.04 - the normal Ubuntu installer (ubiquity) has been offering to install Wubi when it detects all four primary partitions are used (on a MBR formatted disk). It STILL will do this with 15.04. There is still a Wubi.exe on the 15.04 ISO (it happens to be the broken one from 14.10) and that's enough for ubiquity's logic to be triggered.
So this gets me to my point (eventually). I get it that Wubi should be dropped - no one is willing to support it... But can someone remove it as well?!
Let's just consider for a moment that Wubi has actually been fully fixed. It runs on 14.04, 14.10, 15.04. It evens runs on EFI systems. All these patches have been submitted by the hardworking ubuntuforums.org user hakuna_matata.
So it's not like they can't actually fix it. And of course they could remove it properly, but no.
For most people try to avoid Wubi. Don't put Ubuntu DVD's or USB sticks into your Windows computer (or if you do don't let the autorun application run). It's securely signed by Canonical, but this doesn't mean it's fit to run (it's not). Frankly, I'd be embarrassed to be associated with a company that signs something that rubbish.
If you're someone who really is sure they want Wubi, then use hakuna_matata's versions available here. Obviously I can't vouch for .exe files you pull from drop box, but I've built and run them from the code published on launchpad. You can build Wubi as well: I have a post on how to compile Wubi on this blog which you can do from an Ubuntu VM on Windows, for instance. Again, not sure that this is really anyone's cup of tea, but ... that's how you can do it.