Sorry-I guess I latched onto what was probably a too simplistic and perhaps even irrelevant problem to ask my own questions without adding any additional information about what exactly I was looking for in an answer. I just havent fared well asking about it in other threads.
My initial assumption was actually koto, but the reasoning was more from just having a feel for that kind of sentence rather than understanding why it couldn't be mono instead.
I'm not using any one principal text book right now. Using both the Kanzen Master and Unicom JLPT 2kyuu practice series,' intermediate guide to japanese grammar, among other textbooks/study materials.
There was never confusion about these kind of sentences before I learned the use of もの that is in the following sentences.
１）年を取るとだんだん足が弱くなるものです。 and
２）今日でもう５日間雨が降り続いている。全くよく降るものです。
In Unicom's 実力アップ日本語能力試験文法編 book, these two sentences are classified differently;
the first is defined as 一般的なこと ・ 自然のこと ・ 普通のことに使う
the second: 本当に～ 実に～ (驚きや感心した気持ちを言う表現）
Without a teacher and these pretty poor explanations, I only have example sentences to try to figure it out on my own, and with mono I have not been able to do it.
Also, I don't understand the difference between ～というものです and ~と言うことです。