There are many ways to define 'professional', in almost all of them it comes down really to details and polish. Having something 'work' is certainly a benefit, but just having it work doesn't make it professional.
As an extreme example, I think nearly anyone can mow a lawn, however, even though the same exact tools are available to anyone who would undertake such a task, there is a difference between the look produced by someone who just cuts the grass, and someone that cuts the grass, cleans up the extraneous clippings, edges the lot, etc.
Joe Shmoe got the lawn cut, certainly, but the 'Super Spiffy Lawncare Company' left the lawn cut with a professional look.
While I have no idea what JackieBlue1970 was referring to specifically (or even generally), there are plenty of improvements just in the visual department that would make the IDE (past and current) far more professional looking. Just look at how it matured from it's own time span. Mc was certainly usable, but looks almost like a child constructed it, compared to Rev. 1.1.
There are a LOT of details like that, that ruin first impressions, or even long standing impressions. Menu items being cut off (or worse, misspelled), rounded button borders that aren't rounded in places, palettes that override other palettes, dictionary that works (or not) depending on OS, sound, video, the list goes on and on.
You *can* look at any one of those things, and say "Huh, well, everything has quirks!", but when they pile up so far, it is no longer just 'quirky', it begins to feel like it is not representing a professional product.
I hope that the above does not hurt anyone's feelings, it is not intended as a slam against anyone, just an observation and an attempt at what I am sure was an unnecessary explanation.