Is there any reason for numeric rather than int in T-SQL?

Perhaps they're used to working with Oracle?

All numeric types including ints are normalized to a standard single representation among all platforms.

There are many reasons to use numeric - for example - financial data and other stuffs which need to be accurate to certain decimal places. However for the example you cited above, a simple int would have done.

Perhaps sloppy programmers working who didn't know how to to design a database ?

Before you take things too seriously, what is the data storage requirement for each row or set of rows for this item?

Your observation is correct, but you probably don't want to present it too strongly if you're reducing storage from 5000 bytes to 4090 bytes, for example.

You don't want to blow your credibility by bringing this up and having them point out that any measurable savings are negligible. ("Of course, many of our lesser-experienced staff also make the same mistake.")

Can you fill in these blanks?

with the data type change, we use    ____ bytes of disk space instead of ____    ____ ms per query instead of ____    ____ network bandwidth instead of ____    ____ network latency instead of ____

That's the kind of thing which will give you credibility.