icing on the cake

Reader's Digest １月号の記事　"My Story" に次の様に出てきた "icing on the cake" は以前何かで見たことのある表現ですが思い出せません。
My family moved to the suburb of Denistone in Sydney in 1961, when I was eight years old. As we had travelled a bit prior to that, for me living in a cul-de-sac street with a big park at the end was heaven. Half the park was bush, and the track that ran through it was the icing on the cake.
慣用句の様な "icing on the cake" の意味が分からないので辞書で調べます。
・Oxford English Dictionary: An attractive but inessential addition or enhancement: being a scientist is enjoyable, and winning a Nobel is icing on the cake
・Cambridge English Dictionary: something that makes a good situation even better: I was just content to see my daughter in such a stable relationship but a grandchild, that really was the icing on the cake.
・Cambridge Dictionary of American Idioms: something good that is added to another good thing He was delighted to have his story published -- getting paid for it was just icing on the cake.
何故この様な意味になるのかちょっと不思議な気がするので更に調べるとWoodward English に次の説明がありました。
First, before we look at the meaning of this idiom, what is icing?
Icing = a sugary substance used as coating on cakes or cookies (biscuits) to make them look better or to enhance its flavour.
なるほど、これで納得です。しかし、シュガーコーティングした菓子は私は苦手です。