Michael Spivak answered:When I typeset $p_1p_2\ldots p_n$ the subscripts 1 and 2 look too large when placed next to the p. To compensate for this I use $p_{{}_1}p_{{}_2}\ldots p_n$ to use 2nd order subscripts (the n looks OK as a subscript). Is there a better way to do this?
To get this effect use $p_{\scriptscriptstyle1} ... instead of $p_{{}_1}... so that the tiny 1 won't be so low (and don't do this with the n as you noted). However, I wouldn't agree that $p_1p_2 ... has 1 and 2 that are too large; it's just that 1 and 2 are large symbols---$p_H is much more of a problem!
In CM the problem is just as apparent, even more so, in fact. I believe if
you look in various math books you will see things like $p_1p_2$ that never bothered you before you became a type maven!