The reason is that omitted multiplication symbols imply a quantity after the operation. The expression '2a' does not mean the quantity '2' multiplied by the quantity 'a' at all. It means the single quantity obtained after the multiplication. It means what will now have to be written with parentheses, (2a), on newer calculators. Likewise the quantity 2π implies no operation of multiplication at all. Rather it means the single quantity of radians in one circle. It has nothing at all to do with the quantity '2' separated out of the expression. Engineers need 2π in quite many calculations. It will now require thousands of pages with 2π to be rewritten with (2π), else the new calculators might rip the '2' off the quantity and use it separately in some preceding operation.
In many cases it won't make any difference if you mean the single quantity '2a' or the quantity '2' times the quantity 'a' since they are equal after the multiplication. The coincidence is the likely cause of confusion. The clearly incorrect interpretation of implied "multiplication" usually works as well as the clearly correct interpretation of implied "quantity."
The problem arises in longer expressions. Assume a = 12; b = 8; and 2a = 3b = 24.
Now consider the expression 48 ÷ 2a and the expression 48 ÷ 3b.
Since we know 2a = 3b the divisions above should also be equal. They are if you treat 2a and 3b as quantities. The correct answer is 2 in both cases. They are not if you "imply multiplications." The new calculators rip the 2 off the quantity and divide that first 48/2 = 24 then multiply by 12 yielding 288. Likewise the 3 gets ripped off then 48/3 = 16 is multiplied by 8 yielding 128, which is not the same as 288.
Now suppose you were working with the number of radians in a circle as many engineers, myself included, often do.
Can you rip the '2' off the 'π'?
No. Older calculators would do fine and readily recognize '2π' as a single quantity and not rip the '2' off. To get the correct answer with the newer calculators that "imply multiplication" you must add parentheses thus 48 ÷ (2π).
No, it absolutely makes no sense. It takes longer to write and longer to compute. It makes file sizes larger. If for some bizarre reason you need to indicate the '2' may be ripped off you only need '2×π,' three characters not four.
If asked what omitted multiplication signs "imply" the wrong answer is "multiplication" the right answer is the "quantity" obtained from the multiplication. There is no "implied multiplication." If your school accepts the new calculators' notation, your school is wrong.
If you hear that there is "no concensus" what omitted multiplication symbols mean it is only true in the sense of asking people who shouldn't be asked. Anyone who believes omitted multiplication symbols "imply multiplication" should be fired from any position of responsibility for engineering, mathematics or teaching.
You should. If you don't we might consider a class action lawsuit. The implication of "multiplication" being ridiculous as it is the problem should be fixed one way or another soon. They might make calculators that have a means to switch from implied "multiplication" to implied "quantity," but I don't see any use at all for implied multiplication.
I'm sorry I didn't find out about the new calculators sooner. My old ones still work fine. I only found out about the change in an internet discussion group in April 2012.
It might always be true that you should not use any internet website for homework or any equipment for homework unless specifically directed by your teachers. If however your teachers direct you to use sites or equipment with nonstandard practices for homework, you should raise the issue with your educational institution's administration for a sensible explanation.