Very interesting revelations. Surprised this hasn't been more widely publicized - I can't even find the new article in Haaretz, which seems odd.
In a nutshell, it appears the prosecution's case was almost entirely dependent upon the evidence of the victim - a reluctant victim with a troubled past for whom giving testimony was very difficult. The prosecution lost faith in her ability to testify and secure a conviction, and so a plea agreement was reached for the lesser offence of rape by deception, which formed the basis for conviction and sentencing.
Almost all of the victim's testimony (on the issue of consent at least) was excluded from the plea deal and the sentencing process, which resulted in the 18 month sentence for the accused. As far as the court was concerned there was no forced sexual intercourse, only consensual intercourse obtained by lies.
This is a tough call for the prosecution for a number of reasons, which should be obvious.
I would still suggest it sets an ugly legal precedent, regardless of this new background information.
It strips away any sympathy for the convicted man though.
Edit: Found one garbled
opinion piece in Haaretz now...