Shíèrge xiǎoshí shífēnzhōng

In Shíèrge xiǎoshí shífēnzhōng  why does 'hour', but not 'minute' have the classifier 'ge'?

One of my references says that minute 分钟 (fēnzhōng) is a quasi-counter, i.e. a noun that acts as its own counter and so use of another counter is prohibited.  Hour 小时 (xiǎoshí) and week 星期 (xīngqí) are special quasi-counters and as such, use of the 个(ge) is optional.  Other quasi-counters are year and day.