I think it could be a good idea in a lot of cases where post album singles struggle to climb up and get lost/forgotten about, if it can get high up in the chart it will stand a good chance of getting more exposure anyway, as opposed to entering lowly and falling away.

'How Long Will I Love You' is STILL unavailable to buy as an individual track from the 'Halcyon Days' album on iTunes, you can only buy it through the specific single version. That suggests to me that the reason they released it how they did was because there would've been a problem getting the royalties to Children in Need if it wasn't set up as a separate download, rather than it being a ploy to maximize the song's peak.

I assumed it was released in this way so it could be pre-ordered, and they've left the album version album only as not to split sales between two versions.